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A117105 Sums of three positive heptagonal numbers A000566. 1

%I

%S 3,9,15,20,21,26,32,36,37,42,43,48,53,54,57,59,63,69,70,74,75,80,83,

%T 86,89,90,91,95,96,100,102,106,107,111,114,116,116,116,117,120,122,

%U 123,123,126,128,131,133,137,143,144,147,148,149,150,153,154,156,162,163,164,165,167

%N Sums of three positive heptagonal numbers A000566.

%C 7 is the only prime heptagonal number. Primes which are sums of two positive heptagonal numbers include: {2, 19, 41, 73, 89, 113, 149, 167, 193, 223, 229, 269, 293, 337, 347, 367, 383, ...}. Primes which are sums of three positive heptagonal numbers include: {3, 37, 43, 53, 59, 83, 89, 107, 131, 137, 149, 163, 167, 173, 191, 197, 211, 227, 241, 251, 257, 263, 271, ...}.

%F {a(n)} = {A000566} + {A000566} + {A000566} = {a*(5*a-3)/2 + b*(5*b-3)/2 + c*(5*c-3)/2} \ {A000566}.

%Y Cf. A000566, A000040, A000326, A003679, A064826, A117065.

%K easy,nonn

%O 1,1

%A _Jonathan Vos Post_, Apr 18 2006

%E Missing 106 and 131 added by _Giovanni Resta_, Jun 15 2016

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Last modified May 24 17:09 EDT 2019. Contains 323533 sequences. (Running on oeis4.)