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A155575 Intersection of A000404 and A154778: N = a^2 + b^2 = c^2 + 5d^2 for some positive integers a,b,c,d. 1

%I

%S 29,41,45,61,89,101,109,116,145,149,164,180,181,205,225,229,241,244,

%T 245,261,269,281,305,349,356,369,389,401,404,405,409,421,436,445,449,

%U 461,464,505,509,521,541,545,549,569,580,596,601,641,656,661,701,709,720

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

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

%o (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}

%o for( n=1,999, isA155575(n) & print1(n","))

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

%K easy,nonn

%O 1,1

%A _M. F. Hasler_, Jan 25 2009

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Last modified June 12 07:43 EDT 2021. Contains 344943 sequences. (Running on oeis4.)