A269839 Integers n such that the sum of the first n cubes (A000537) is the sum of 2 positive cubes.

2, 49, 4557, 13689, 18816, 86015, 159249, 226981, 1368912, 2112278

Offset

1,1

Comments

In other words, integers n such that (1+2+3+...+n)^2 = x^3 + y^3 where x and y are positive integers, is soluble.

Links

Table of n, a(n) for n=1..10.

Example

49 is a term because A000537(49) = 1^3 + 2^3 + ... + 48^3 + 49^3 = 1500625 = 70^3 + 105^3.
4557 is a term because A000537(4557) = 1^3 + 2^3 + ... + 4556^3 + 4557^3 = 107856595472409 = 11620^3 + 47369^3.

Prog

(PARI) isA003325(n) = for(k=1, sqrtnint(n\2, 3), ispower(n-k^3, 3) && return(1));
for(n=0, 1e7, if(isA003325((n*(n+1)/2)^2), print1(n, ", ")));

Crossrefs

Cf. A000537, A003325.

Sequence in context: A243720 A210922 A257742 * A088067 A145676 A335406

Adjacent sequences: A269836 A269837 A269838 * A269840 A269841 A269842

Keyword

nonn,more

Author

Altug Alkan, Mar 06 2016

Extensions

a(6)-a(10) from Chai Wah Wu, Mar 08 2016

Status

approved