_M. F. Hasler (www.univ-ag.fr/~mhasler), _, Jan 25 2009

OEIS Server: https://oeis.org/edit/global/1815

easy,nonn,new

M. F. Hasler (MHasler(AT)www.univ-ag.fr/~mhasler), Jan 25 2009

(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}

easy,nonn,new

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

1,1

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

(PARI) isA155575(n, /* optional 2nd arg allows 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", "))

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

easy,nonn

M. F. Hasler (MHasler(AT)univ-ag.fr), Jan 25 2009

approved