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A268445 Integers n such that A005897(n) is the sum of two nonzero squares. 0

%I

%S 1,2,4,6,7,8,9,12,15,16,20,22,23,26,28,30,34,36,40,41,44,47,49,50,54,

%T 55,56,57,58,63,64,65,68,70,78,82,84,86,89,94,97,98,102,103,104,105,

%U 106,111,112,113,118,120,126,127,132,135,142,143,145,146,148,151,152,153,154,156

%N Integers n such that A005897(n) is the sum of two nonzero squares.

%C Integers n such that number of points on surface of a 3-dimensional cube in which each face has a square grid of dots drawn on it (with n+1 points along each edge, including the corners) is the sum of two nonzero squares.

%e 1 is a term because A005897(1) = 8 = 2^2 + 2^2.

%e 2 is a term because A005897(2) = 26 = 1^2 + 5^2.

%e 4 is a term because A005897(4) = 98 = 7^2 + 7^2.

%e 6 is a term because A005897(6) = 218 = 7^2 + 13^2.

%o (PARI) is_a000404(n) = {for( i=1, #n=factor(n)~%4, n[1, i]==3 && n[2, i]%2 && return); n && ( vecmin(n[1, ])==1 || (n[1, 1]==2 && n[2, 1]%2))}

%o a005897(n) = if(n, 6*n^2+2, 1);

%o for(n=0, 200, if(is_a000404(a005897(n)), print1(n, ", ")));

%Y Cf. A000404, A005897.

%K nonn,easy

%O 1,2

%A _Altug Alkan_, Feb 04 2016

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Last modified January 21 19:05 EST 2022. Contains 350480 sequences. (Running on oeis4.)