|
%I #7 Feb 02 2017 02:42:09
%S 21,22,55,129,511,770,1070,1071,1074,1434,1708,1914,2721,2926,3080,
%T 4195,4464,4814,4879,5236,5907,6086,6114,7228,7831,8029,8289,9086,
%U 10149,10547,11145,12305,12621,13348,14993,15012,16212,17670,19513,20020,20083
%N Numbers n such that sigma(n^3) is the sum of two positive cubes.
%C 265247 is the first term that is prime; sigma(265247^3) = 18661780598460480 = 48432^3 + 264708^3. In other words, the equation (1 + p)*(1 + p^2) = a^3 + b^3 where p is prime and a, b > 0, is soluble.
%H Chai Wah Wu, <a href="/A281364/b281364.txt">Table of n, a(n) for n = 1..700</a>
%e 21 is a term because sigma(21^3) = 16000 = 20^3 + 20^3.
%o (PARI) isA003325(n) = for(k=1, sqrtnint(n\2, 3), ispower(n-k^3, 3) && return(1));
%o lista(nn) = for(n=1, nn, if(isA003325(sigma(n^3)), print1(n, ", ")));
%Y Cf. A000203, A000578, A003325, A175926.
%K nonn
%O 1,1
%A _Altug Alkan_, May 01 2016
|
