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Search: id:A002100
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| A002100 |
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a(n) = number of partitions of n into semiprimes (more precisely, number of ways of writing n as a sum of products of 2 distinct primes).
(Formerly M0205 N0076)
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+0
2
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| 0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 1, 0, 1, 1, 1, 0, 1, 0, 2, 2, 2, 0, 2, 1, 3, 2, 3, 1, 4, 2, 4, 3, 5, 4, 7, 3, 6, 5, 8, 6, 10, 6, 10, 9, 12, 9, 15, 11, 16, 14, 18, 14, 22, 19, 25, 22, 27, 23, 33, 29, 36, 33, 40, 38, 49, 43, 53, 51, 61, 57, 71, 64, 77, 76, 89, 86, 102, 96, 113, 111, 128, 125
(list; graph; listen)
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OFFSET
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1,20
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REFERENCES
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L. M. Chawla and S. A. Shad, On a restricted partition function t(n) and its table, J. Natural Sciences and Mathematics, 9 (1969), 217-221. Math. Rev. 41 #6761.
N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
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T. D. Noe, Table of n, a(n) for n=1..1000
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EXAMPLE
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a(20) = 2: 20 = 2*3 + 2*7 = 2*5 + 2*5.
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PROGRAM
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(PARI) a(n)=polcoeff(1/prod(k=1, n, if(issquarefree(k)*if(omega(k)-2, 0, 1), 1-z^k, 1))+O(z^(n+1)), n)
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CROSSREFS
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Sequence in context: A028930 A112792 A138319 this_sequence A108352 A036476 A104994
Adjacent sequences: A002097 A002098 A002099 this_sequence A002101 A002102 A002103
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KEYWORD
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nonn
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com).
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EXTENSIONS
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More terms from Benoit Cloitre (benoit7848c(AT)orange.fr), Jun 01 2003
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