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 A117105 Sums of three positive heptagonal numbers A000566. 1
 3, 9, 15, 20, 21, 26, 32, 36, 37, 42, 43, 48, 53, 54, 57, 59, 63, 69, 70, 74, 75, 80, 83, 86, 89, 90, 91, 95, 96, 100, 102, 106, 107, 111, 114, 116, 116, 116, 117, 120, 122, 123, 123, 126, 128, 131, 133, 137, 143, 144, 147, 148, 149, 150, 153, 154, 156, 162, 163, 164, 165, 167 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS 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, ...}. LINKS FORMULA {a(n)} = {A000566} + {A000566} + {A000566} = {a*(5*a-3)/2 + b*(5*b-3)/2 + c*(5*c-3)/2} \ {A000566}. CROSSREFS Cf. A000566, A000040, A000326, A003679, A064826, A117065. Sequence in context: A071347 A093414 A123998 * A261190 A282031 A307202 Adjacent sequences:  A117102 A117103 A117104 * A117106 A117107 A117108 KEYWORD easy,nonn AUTHOR Jonathan Vos Post, Apr 18 2006 EXTENSIONS Missing 106 and 131 added by Giovanni Resta, Jun 15 2016 STATUS approved

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Last modified April 18 06:48 EDT 2019. Contains 322209 sequences. (Running on oeis4.)