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A078097 Least m such that P - m is prime, where P is the n-th perfect number. 0
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; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Some of the larger entries may only correspond to probable primes.

LINKS

Table of n, a(n) for n=1..26.

MATHEMATICA

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}]

CROSSREFS

Cf. A061644, A000396, A000043.

Sequence in context: A076407 A134701 A291655 * A285243 A282209 A082476

Adjacent sequences:  A078094 A078095 A078096 * A078098 A078099 A078100

KEYWORD

hard,more,nonn

AUTHOR

Jason Earls, Dec 01 2002

EXTENSIONS

Edited and extended by Robert G. Wilson v, Dec 03 2002

a(19)-a(26) from Donovan Johnson, Feb 22 2008

STATUS

approved

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Last modified June 19 13:11 EDT 2019. Contains 324222 sequences. (Running on oeis4.)