A155568 - OEIS

%I #3 Jul 14 2012 11:32:23

%S 0,1,4,8,9,16,25,29,32,36,37,49,53,64,72,81,100,109,113,116,121,128,

%T 137,144,148,149,169,193,196,197,200,212,225,232,233,256,261,277,281,

%U 288,289,296,317,324,333,337,361,373,389,392,400,401,421,424,436,441,449

%N Intersection of A001481 inter A020670: N = a^2 + b^2 = c^2 + 7d^2 for some integers a,b,c,d.

%C Contains A155578 as a subsequence (obtained by restricting a,b,c,d to be nonzero). Also contains A000290 (squares) as subsequence.

%o (PARI) isA155568(n,/* use optional 2nd arg to get other analogous sequences */c=[7,1]) = { for(i=1,#c, for(b=0,sqrtint(n\c[i]), issquare(n-c[i]*b^2) & next(2)); return);1}

%o for( n=0,500, isA155568(n) & print1(n","))

%Y Cf. A001481, A002479, A003136, A002481, A020668 ff.

%K easy,nonn

%O 1,3

%A _M. F. Hasler_, Jan 25 2009