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Numbers which are the sum of two positive cubes and divisible by 31.
6

%I #13 Jun 13 2020 00:52:08

%S 217,341,1395,1674,1736,2728,4123,5425,5642,5859,6293,7471,7657,8029,

%T 8587,9207,9269,9331,10261,11160,11377,12679,12896,13392,13888,14167,

%U 14911,15841,16120,17577,17701,19747,20026,21824,21979,24149,24397

%N Numbers which are the sum of two positive cubes and divisible by 31.

%H Vincenzo Librandi, <a href="/A102658/b102658.txt">Table of n, a(n) for n = 1..1000</a>

%t upto[n_] := Block[{t}, Union@ Reap[ Do[If[Mod[t = x^3 + y^3, 31] == 0, Sow@t], {x, n^(1/3)}, {y, Min[x, (n - x^3)^(1/3)]}]][[2, 1]]]; upto[24500] (* _Giovanni Resta_, Jun 12 2020 *)

%Y Cf. A003325, A101421 (divisible by k=7), A101852 (k=11), A094447 (k=13), A099178 (k=17), A102619 (k=19), A101806 (k=23), A224483 (k=29), A102618 (k=37).

%K nonn,easy

%O 1,1

%A Jun Mizuki (suzuki32(AT)sanken.osaka-u.ac.jp), Feb 02 2005