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A100013 Number of prime factors in n!+7 (counted with multiplicity). 1
3, 3, 2, 1, 1, 1, 1, 3, 3, 3, 3, 2, 3, 3, 4, 2, 2, 3, 3, 5, 5, 5, 3, 4, 3, 2, 4, 5, 5, 4, 7, 6, 4, 4, 7, 2, 5, 4, 7, 4, 5, 3, 4, 6, 5, 4, 3, 3, 5, 6, 3, 5, 6, 3, 3, 7, 4, 5, 5, 2, 4, 4, 5, 4, 2, 4, 3, 5, 2, 5, 7, 4, 7, 5, 5, 3, 5, 4, 6, 6, 8, 5 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

REFERENCES

C. Caldwell and H. Dubner, "Primorial, factorial and multifactorial primes," Math. Spectrum, 26:1 (1993/4) 1-7.

LINKS

Table of n, a(n) for n=0..81.

Chris Caldwell, multifactorial prime (another Prime Pages' Glossary entries).

Ken Davis, Status of Search for Multifactorial Primes.

Sean A. Irvine, Factorizations of n!+7

EXAMPLE

Example 1!+7 = 2^3 so a(1) = 3.

a(3) = a(4) = a(5) = a(6) = 1 because 3!+1 = 13, 4!+7 = 31, 5!+1 = 127, 6!+7 = 727 and these are all primes. a(11) = a(15) = a(16) = a(25) = a(35) = a(59) = 2 because 11!+7 = 39916807 = 7 * 5702401, 15!+7 = 1307674368007 = 7 * 186810624001, 16!+7 = 20922789888007 = 7 * 2988969984001, 25!+7 = 15511210043330985984000007 = 7 * 2215887149047283712000001, 35!+7 = 10333147966386144929666651337523200000007 = 7 *

1476163995198020704238093048217600000001 and 59!+7 = 138683118545689835737939019720389406345902876772687432540821294940160000000000007 = 7 * 19811874077955690819705574245769915192271839538955347505831613562880000000000001 are all semiprimes.

CROSSREFS

Cf. A002981, A037083, A037083, A085150, A085148, A085146, A062701, A055487, A062702.

Sequence in context: A254411 A056223 A261143 * A065744 A016455 A278702

Adjacent sequences:  A100010 A100011 A100012 * A100014 A100015 A100016

KEYWORD

easy,nonn

AUTHOR

Jonathan Vos Post, Nov 18 2004

EXTENSIONS

More terms from Sean A. Irvine, Sep 20 2012

STATUS

approved

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Last modified October 26 05:25 EDT 2021. Contains 348256 sequences. (Running on oeis4.)