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Search: id:A078097
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| A078097 |
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Least m such that P - m is prime, where P is the n-th perfect number. |
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+0
1
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| 1, 5, 5, 5, 5, 17, 9, 65, 93, 129, 627, 111, 407, 795, 377, 1509, 257, 5207, 1233, 8537, 3917, 20253, 4613, 15435, 5619, 43823
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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Some of the larger entries may only correspond to probable primes.
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MATHEMATICA
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e (* from A000043 *) = {2, 3, 5, 7, 13, 17, 19, 31, 61, 89, 107, 127, 521, 607, 1279, 2203, 2281, 3217, 4253, 4423, ...}; PrevPrim[n_] := Block[{k = n - 1}, While[ !PrimeQ[k], k-- ]; k]; Do[p = 2^(e[[n]] - 1)*(2^e[[n]] - 1); Print[p - PrevPrim[p]], {n, 1, 20}]
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CROSSREFS
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Cf. A061644, A000396, A000043.
Adjacent sequences: A078094 A078095 A078096 this_sequence A078098 A078099 A078100
Sequence in context: A003870 A076407 A134701 this_sequence A082476 A024729 A046271
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KEYWORD
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hard,more,nonn
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AUTHOR
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Jason Earls (zevi_35711(AT)yahoo.com), Dec 01 2002
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EXTENSIONS
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Edited and extended by Robert G. Wilson v (rgwv(AT)rgwv.com), Dec 03 2002
a(19)-a(26) from Donovan Johnson (donovan.johnson(AT)yahoo.com), Feb 22 2008
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