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Search: id:A100013
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| A100013 |
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Number of prime factors in n!+7 (counted with multiplicity). |
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+0
1
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| 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
(list; graph; listen)
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OFFSET
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0,1
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REFERENCES
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C. Caldwell and H. Dubner, "Primorial, factorial and multifactorial primes," Math. Spectrum, 26:1 (1993/4) 1-7.
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LINKS
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Chris Caldwell, multifactorial prime (another Prime Pages' Glossary entries).
Ken Davis, Status of Search for Multifactorial Primes.
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EXAMPLE
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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.
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CROSSREFS
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Cf. A002981, A037083, A037083, A085150, A085148, A085146, A062701, A055487, A062702.
Sequence in context: A106449 A097278 A056223 this_sequence A065744 A016455 A060574
Adjacent sequences: A100010 A100011 A100012 this_sequence A100014 A100015 A100016
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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), Nov 18 2004
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