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Search: id:A114548
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| A114548 |
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Numbers n such that n-th heptagonal number is 3-almost prime. |
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1
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| 3, 8, 11, 19, 20, 25, 28, 37, 43, 52, 58, 59, 67, 68, 70, 77, 82, 83, 85, 86, 89, 92, 98, 106, 110, 116, 124, 130, 131, 133, 137, 139, 142, 149, 157, 161, 169, 172, 179, 181, 182, 185, 188, 190, 193, 202, 206, 209, 211
(list; graph; listen)
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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 3-almost prime. n such that A000566(n) is an element of A014612. n such that A001222(A000566(n)) = 3. n such that A001222(n*(5*n-3)/2) = 3.
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EXAMPLE
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a(1) = 3 because Hep(3) = 3*(5*3-3)/2 = 18 = 2 * 3^2 is 3-almost prime.
a(2) = 8 because Hep(8) = 8*(5*8-3)/2 = 148 = 2^2 * 37 is 3-almost prime.
a(3) = 11 because Hep(11) = 11*(5*11-3)/2 = 286 = 2 * 11 * 13 is 3-almost prime.
a(17) = 82 because Hep(82) = 82*(5*82-3)/2 = 16687 = 11 * 37 * 41 is 3-almost prime (and 3-brilliant).
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CROSSREFS
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Cf. A000040, A000566, A001222, A001358, A014612, A099153.
Sequence in context: A058572 A154485 A105410 this_sequence A022121 A070073 A058565
Adjacent sequences: A114545 A114546 A114547 this_sequence A114549 A114550 A114551
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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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