A155575 Intersection of A000404 and A154778: N = a^2 + b^2 = c^2 + 5d^2 for some positive integers a,b,c,d.

29, 41, 45, 61, 89, 101, 109, 116, 145, 149, 164, 180, 181, 205, 225, 229, 241, 244, 245, 261, 269, 281, 305, 349, 356, 369, 389, 401, 404, 405, 409, 421, 436, 445, 449, 461, 464, 505, 509, 521, 541, 545, 549, 569, 580, 596, 601, 641, 656, 661, 701, 709, 720

Offset

1,1

Comments

Subsequence of A155565 (where a,b,c,d may be zero).

Links

Table of n, a(n) for n=1..53.

Prog

(PARI) isA155575(n, /* optional 2nd arg allows us to get other sequences */c=[5, 1]) = { for(i=1, #c, for(b=1, sqrtint((n-1)\c[i]), issquare(n-c[i]*b^2) & next(2)); return); 1}
for( n=1, 999, isA155575(n) & print1(n", "))

Crossrefs

Cf. A000404, A154777, A092572, A097268, A154778, A155716, A155717, A155560-A155578.

Sequence in context: A242555 A101007 A253252 * A229059 A330653 A125516

Adjacent sequences: A155572 A155573 A155574 * A155576 A155577 A155578

Keyword

easy,nonn

Author

M. F. Hasler, Jan 25 2009

Status

approved