Taxicab Numbers - 4th powers
The nth Taxicab number is the smallest integer
that can be written as the sum of two positive cubes in n
different ways. It is known that there are numbers
expressible in as the sum of two cubes in any number of ways.
Can we extend the concept of Taxicab numbers to higher powers?
Jaroslaw Wroblewski and Stuart Gascoigne proved that for all
powers, there are numbers expressible as the sum of (n+1)
nth powers in m ways, for
any value of m. (see proof).Can we use less than n+1
powers? Can we find 3-way or 4-way sums even if m-way sums do not
exist? I will use the notation Taxicab(n,p,m) to
denote the smallest number expressible in m ways
as the sum of p nth powers.
The obvious first step is to try and find numbers expressible
as the sum of two fourth powers in several ways. The smallest
number expressible as the sum of two fourth powers in two ways is
635318657 = 1334 + 1344 =
1584 + 594
found by Euler.
If there is a number expressible as the sum of
two fourth powers in three ways it is Taxicab(4,2,3) > 2.6x1026
(Stuart Gascoigne).
Can we use sums of three fourth powers? The
answer is yes. Hardy and Wright prove that there are numbers
expressible as the sums of three fourth powers in any number of
ways.
Below are listed the first 18 Taxicab(4,3,m)
numbers. Interestingly, we can note that Taxicab(4,3,5) includes
a zero term. Also note that the series goes from 10 to 12 to 16
to 18, missing out the odd terms.
Taxicab(4,3,1) = 1
= 14 + 04 + 04
Taxicab(4,3,2) = 2673
= 74 + 44 + 24
= 64 + 64 + 34
Taxicab(4,3,3) = 811538
= 294 + 174 + 124
= 284 + 214 + 74
= 274 + 234 + 44
Taxicab(4,3,4) = 5978882
= 484 + 254 + 234
= 474 + 324 + 154
= 454 + 374 + 84
= 434 + 404 + 34
Taxicab(4,3,5) = 137149922
= 1054 + 564 + 494
= 1044 + 654 + 394
= 994 + 804 + 194
= 964 + 854 + 114
= 914 + 914 + 04
Taxicab(4,3,6) = 292965218
= 1274 + 664 + 614
= 1264 + 774 + 494
= 1234 + 894 + 344
= 1214 + 944 + 274
= 1194 + 984 + 214
= 1114 + 1094 + 24
Taxicab(4,3,7) = 779888018
= 1674 + 384 + 94
= 1624 + 894 + 734
= 1614 + 984 + 634
= 1584 + 1114 + 474
= 1574 + 1144 + 434
= 1474 + 1334 + 144
= 1424 + 1394 + 34
Taxicab(4,3,8) = 5745705602
= 2674 + 1454 + 1224
= 2654 + 1634 + 1024
= 2634 + 1734 + 904
= 2624 + 1774 + 854
= 2554 + 1974 + 584
= 2504 + 2074 + 434
= 2434 + 2184 + 254
= 2334 + 2304 + 24
Taxicab(4,3,10) = 49511121842
= 4584 + 2334 + 2254
= 4574 + 2554 + 2024
= 4554 + 2734 + 1824
= 4474 + 3104 + 1374
= 4424 + 3254 + 1174
= 4414 + 3224 + 1754
= 4384 + 3354 + 1034
= 4274 + 3574 + 704
= 4134 + 3784 + 354
= 4034 + 3904 + 134
Taxicab(4,3,12) = 281539574498
= 7074 + 3714 + 3364
= 7044 + 4114 + 2934
= 7014 + 4324 + 2694
= 6994 + 4434 + 2564
= 6964 + 4574 + 2394
= 6934 + 4694 + 2244
= 6794 + 5114 + 1684
= 6644 + 5434 + 1214
= 6564 + 5574 + 994
= 6494 + 5684 + 814
= 6324 + 5914 + 414
= 6164 + 6094 + 74
Taxicab(4,3,16) = 7865870969138
= 16264 + 8294 + 7974
= 16224 + 9114 + 7114
= 16214 + 9224 + 6994
= 16194 + 9414 + 6784
= 16114 + 9974 + 6144
= 16014 + 10474 + 5544
= 15794 + 11264 + 4534
= 15784 + 11294 + 4494
= 15714 + 11494 + 4224
= 15534 + 11944 + 3594
= 15494 + 12034 + 3464
= 15034 + 12894 + 2144
= 14944 + 13034 + 1914
= 14814 + 13224 + 1594
= 14474 + 13664 + 814
= 14344 + 13814 + 534
Taxicab(4,3,18) = 47580188090162
= 25484 + 13654 + 11834
= 25454 + 14134 + 11324
= 25404 + 14674 + 10734
= 25354 + 15084 + 10274
= 25254 + 15724 + 9534
= 25234 + 15834 + 9404
= 25154 + 16234 + 8924
= 24924 + 17154 + 7774
= 24874 + 17324 + 7554
= 24574 + 18204 + 6374
= 24434 + 18554 + 5884
= 24054 + 19374 + 4684
= 23724 + 19974 + 3754
= 23534 + 20284 + 3254
= 23274 + 20674 + 2604
= 23034 + 21004 + 2034
= 22934 + 21134 + 1804
= 22124 + 22054 + 74
Taxicab(4,3,19) = 101635786393778
= 31734 + 7224 + 1714
= 30834 + 15424 + 15414
= 30824 + 16094 + 14734
= 30784 + 16914 + 13874
= 30664 + 18134 + 12534
= 30594 + 18624 + 11974
= 30374 + 19784 + 10594
= 30174 + 20584 + 9594
= 30024 + 21094 + 8934
= 29834 + 21664 + 8174
= 29674 + 22094 + 7584
= 29574 + 22344 + 7234
= 29344 + 22874 + 6474
= 28914 + 23734 + 5184
= 28634 + 24224 + 4414
= 27934 + 25274 + 2664
= 27634 + 25664 + 1974
= 27274 + 26094 + 1184
= 26984 + 26414 + 574
found by Duncan Moore
Taxicab(4,3,24) = 385427677487762
= 43014 + 22414 + 20604
= 43004 + 22714 + 20294
= 42954 + 23644 + 19314
= 42914 + 24154 + 18764
= 42854 + 24764 + 18094
= 42844 + 24854 + 17994
= 42604 + 26514 + 16094
= 42494 + 27094 + 15404
= 42194 + 28394 + 13804
= 41964 + 29214 + 12754
= 41794 + 29754 + 12044
= 41644 + 30194 + 11454
= 41554 + 30444 + 11114
= 41254 + 31214 + 10044
= 41004 + 31794 + 9214
= 40814 + 32204 + 8614
= 40494 + 32844 + 7654
= 39554 + 34444 + 5114
= 39414 + 34654 + 4764
= 39164 + 35014 + 4154
= 38694 + 35644 + 3054
= 38364 + 36054 + 2314
= 38314 + 36114 + 2204
= 37564 + 36954 + 614
found by Duncan Moore
(This is sequence A085559 from the Online
Encyclopedia of Integer Sequences)
References
G.H. Hardy & E.M. Wright: An introduction
to the theory of numbers 5th edition (1979) p330
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