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Search: id:A114437
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| A114437 |
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Indices of 6-almost prime triangular numbers. |
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1
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| 48, 96, 99, 104, 111, 116, 119, 124, 132, 134, 140, 147, 152, 161, 176, 188, 189, 200, 208, 223, 231, 239, 240, 252, 260, 264, 275, 299, 300, 303, 304, 336, 342, 343, 344, 352, 359, 363
(list; graph; listen)
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OFFSET
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1,1
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LINKS
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Eric Weisstein's World of Mathematics, Triangular Number.
Eric Weisstein's World of Mathematics, Almost Prime.
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FORMULA
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{a(n)} = {k such that A001222(A000217(k)) = 6}. {a(n)} = {k such that k*(k+1)/2 has exactly 6 prime factors, with multiplicity}. {a(n)} = {k such that A000217(k) is an element of A046306}.
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EXAMPLE
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a(1) = 48 because T(48) = TriangularNumber(48) = 48*(48+1)/2 = 1176 = 2^3 * 3 * 7^2 is a 6-almost prime.
a(2) = 96 because T(96) = 96*(96+1)/2 = 4656 = 2^4 * 3 * 97 is a 6-almost prime.
a(18) = 200 because T(200) = 200*(200+1)/2 = 20100 = 2^2 * 3 * 5^2 * 67 is a 6-almost prime.
a(29) = 300 because T(300) = 300*(300+1)/2 = 45150 = 2 * 3 * 5^2 * 7 * 43 is a 6-almost prime.
a(38) = 363 because T(363) = 363*(363+1)/2 = 45150 = 66066 = 2 * 3 * 7 * 11^2 * 13 is a 6-almost prime (363 and 66066 are both palindromatic).
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CROSSREFS
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Cf. A000217, A001222, A046306.
Sequence in context: A044029 A062902 A058229 this_sequence A043418 A031486 A044186
Adjacent sequences: A114434 A114435 A114436 this_sequence A114438 A114439 A114440
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KEYWORD
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easy,nonn
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AUTHOR
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Jonathan Vos Post (jvospost2(AT)yahoo.com), Feb 14 2006
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