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Search: id:A114559
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| A114559 |
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Numbers n such that n-th heptagonal number is 7-almost prime. |
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1
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OFFSET
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1,1
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COMMENT
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Hep(2) = 7 is the only prime heptagonal number.
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LINKS
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Eric Weisstein's World of Mathematics, Heptagonal Number.
Eric Weisstein's World of Mathematics, Almost Prime.
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FORMULA
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n such that Hep(n) = n*(5*n-3)/2 is 7-almost prime. n such that A000566(n) is an element of A046308. n such that A001222(A000566(n)) = 7. n such that A001222(n*(5*n-3)/2) = 7.
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EXAMPLE
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a(1) = 60 because Hep(60) = 60*(5*60-3)/2 = 8910 = 2 * 3^4 * 5 * 11 is 7-almost prime.
a(2) = 63 because Hep(63) = 63*(5*63-3)/2 = 9828 = 2^2 * 3^3 * 7 * 13 is 7-almost prime.
a(3) = 72 because Hep(72) = 72*(5*72-3)/2 = 12852 = 2^2 * 3^3 * 7 * 17 is 7-almost prime.
a(4) = 114 because Hep(114) = 114*(5*114-3)/2 = 32319 = 3^5 * 7 * 19 is 7-almost prime.
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CROSSREFS
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Cf. A000040, A000566, A001222, A001358, A046308.
Sequence in context: A051713 A060225 A124901 this_sequence A112826 A138690 A118155
Adjacent sequences: A114556 A114557 A114558 this_sequence A114560 A114561 A114562
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KEYWORD
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easy,nonn
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AUTHOR
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Jonathan Vos Post (jvospost3(AT)gmail.com), Feb 15 2006
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