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Search: id:A018252
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| A018252 |
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The nonprime numbers (1 together with the composite numbers, A002808). |
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+0
118
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| 1, 4, 6, 8, 9, 10, 12, 14, 15, 16, 18, 20, 21, 22, 24, 25, 26, 27, 28, 30, 32, 33, 34, 35, 36, 38, 39, 40, 42, 44, 45, 46, 48, 49, 50, 51, 52, 54, 55, 56, 57, 58, 60, 62, 63, 64, 65, 66, 68, 69, 70, 72, 74, 75, 76, 77, 78, 80, 81, 82, 84, 85, 86, 87, 88
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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d(n)<>2 (cf. A000005). [From Juri-Stepan Gerasimov (2stepan(AT)rambler.ru), Oct 17 2009]
Number of prime divisors of n (counted with multiplicity)<>1. [From Juri-Stepan Gerasimov (2stepan(AT)rambler.ru), Oct 30 2009]
Largest nonprime<nth composite. [From Juri-Stepan Gerasimov (2stepan(AT)rambler.ru), Oct 29 2009]
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REFERENCES
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G. H. Hardy and E. M. Wright, An Introduction to the Theory of Numbers. 3rd ed., Oxford Univ. Press, 1954, p. 2.
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LINKS
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N. J. A. Sloane, List of nonprimes up to 20000: Table of n, a(n) for n = 1..17738
Unknown, The n-th nonprime.
Eric Weisstein's World of Mathematics, Monica Set
Eric Weisstein's World of Mathematics, Suzanne Set
Index entries for "core" sequences
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FORMULA
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Let b(0)=n+pi(n) and b(n+1)=n+pi(b(n)), with pi(n)=A000720(n); then a(n) is the limit value of b(n). - Floor van Lamoen (fvlamoen(AT)hotmail.com), Oct 08 2001
a(n) = A137621(A137624(n)). - Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Jan 30 2008
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MAPLE
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with(numtheory); sort(convert(convert([ seq(i, i=1..541) ], set) minus convert([ seq(ithprime(i), i=1..100) ], set), list));
seq(`if`(not isprime(n), n, NULL), n=1..88); [From Peter Luschny (peter(AT)luschny.de), Jul 29 2009]
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MATHEMATICA
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NonPrime[n_Integer] := FixedPoint[n + PrimePi[ # ] &, n + PrimePi[n]]; Table[ NonPrime[n], {n, 1, 75} ]
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PROGRAM
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(MAGMA) [n : n in [1..100] | not IsPrime(n) ];
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CROSSREFS
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Cf. A000040, A002808.
Adjacent sequences: A018249 A018250 A018251 this_sequence A018253 A018254 A018255
Sequence in context: A133576 A088224 A002808 this_sequence A141468 A077091 A051035
Cf. A000005, A001222. [From Juri-Stepan Gerasimov (2stepan(AT)rambler.ru), Oct 30 2009]
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KEYWORD
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nonn,nice,easy,core,new
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com).
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