Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #3 Jul 14 2012 11:32:23
%S 0,1,4,5,9,16,20,25,29,36,41,45,49,61,64,80,81,89,100,101,109,116,121,
%T 125,144,145,149,164,169,180,181,196,205,225,229,241,244,245,256,261,
%U 269,281,289,305,320,324,349,356,361,369,389,400,401,404,405,409,421
%N Intersection of A001481 and A020669: N = a^2 + b^2 = c^2 + 5d^2 for some integers a,b,c,d.
%C Contains A155575 as a subsequence (obtained by restricting a,b,c,d to be nonzero). Also contains A000290 (squares) as subsequence.
%o (PARI) isA155565(n,/* use optional 2nd arg to get other analogous sequences */c=[5,1]) = { for(i=1,#c, for(b=0,sqrtint(n\c[i]), issquare(n-c[i]*b^2) & next(2)); return);1}
%o for( n=1,500, isA155565(n) & print1(n","))
%Y Cf. A001481, A002479, A003136, A002481, A020668 ff.
%K easy,nonn
%O 1,3
%A _M. F. Hasler_, Jan 25 2009