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Intersection of A092572 and A154778: N = a^2 + 3b^2 = c^2 + 5d^2 for some positive integers a,b,c,d.
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%I #3 Jul 14 2012 11:32:23

%S 21,36,49,61,84,109,129,144,181,189,196,201,229,241,244,301,309,324,

%T 336,349,381,409,421,436,441,469,489,516,525,541,549,576,601,661,669,

%U 709,721,724,756,769,784,804,829,849,889,900,916,921,964,976,981,1009,1021

%N Intersection of A092572 and A154778: N = a^2 + 3b^2 = c^2 + 5d^2 for some positive integers a,b,c,d.

%C Subsequence of A155570 (where a,b,c,d may be zero).

%o (PARI) isA155710(n,/* use optional 2nd arg to get other analogous sequences */c=[5,3]) = { for(i=1,#c, for(b=1,sqrtint((n-1)\c[i]), issquare(n-c[i]*b^2) & next(2)); return);1}

%o for( n=1,1111, isA155710(n) & print1(n","))

%Y Cf. A000404, A154777, A092572, A097268, A154778, A155716, ...

%K easy,nonn

%O 1,1

%A _M. F. Hasler_, Jan 25 2009