A239971 Least k>1 such that triangular(n) + triangular(n+k) is a square.

8, 4, 10, 16, 22, 6, 34, 40, 14, 52, 58, 8, 16, 76, 82, 24, 94, 100, 106, 10, 23, 124, 20, 136, 142, 25, 36, 160, 22, 12, 178, 184, 55, 46, 202, 208, 54, 220, 226, 34, 56, 14, 26, 31, 262, 36, 274, 66, 49, 89, 28, 304, 65, 316, 76, 16, 48, 84, 346, 352, 358, 86, 50, 376

Offset: 0

Author

Alex Ratushnyak, Mar 30 2014

Keywords

• nonn

Comments

For n>0, a(n) <= 6*n-2 because triangular(n) + triangular(7*n-2) = (5*n-1)^2.

Crossrefs

Cf. A000217, A232177.

Programs

PARI

triangular(n) = n*(n+1)/2;
s=[]; for(n=0, 100, k=2; while(!issquare(triangular(n)+triangular(n+k)), k++); s=concat(s, k)); s \\ Colin Barker, Mar 31 2014