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Search: id:A109823
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| A109823 |
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a(n) is the minimal b >= n such that sum of consecutive integers from n to b is a semiprime. |
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+0
2
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| 3, 4, 7, 4, 8, 6, 8, 11, 9, 10, 15, 13, 16, 14, 15, 17, 18, 20, 20, 23, 21, 22, 35, 25, 25, 26, 28, 29, 32, 32, 36, 33, 33, 34, 35, 38, 42, 38, 39, 42, 45, 43, 44, 50, 46, 46, 48, 53, 49, 53, 51, 54, 56, 59, 55, 62, 57, 58, 60, 61, 62, 62, 68, 65, 65, 67, 70, 71, 69, 71, 72, 73
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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If n is a semiprime, a(n)=n. It is not evident that for any n there is relative a(n), see A109411. For n <1000, the corresponding a(n) exists. Cf. A109824(n) = A109823(n) - n + 1.
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PROGRAM
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(PARI) {issemiprime(n) = local(f); f = factorint(n)[, 2]; sum(i = 1, length(f), f[i]) == 2}{a1(n) = local(s, m); s = n; m = n; while(! issemiprime(s), m++; s += m); m}
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CROSSREFS
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Cf. A109411, A109824.
Sequence in context: A082089 A089961 A161775 this_sequence A071051 A163830 A050197
Adjacent sequences: A109820 A109821 A109822 this_sequence A109824 A109825 A109826
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KEYWORD
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nonn
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AUTHOR
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Zak Seidov (zakseidov(AT)yahoo.com) & Max Alekseyev (maxale(AT)gmail.com), Jul 03 2005
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