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A066247
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Characteristic function of composite numbers: 1 if n is composite else 0.
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13
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0, 0, 0, 1, 0, 1, 0, 1, 1, 1, 0, 1, 0, 1, 1, 1, 0, 1, 0, 1, 1, 1, 0, 1, 1, 1, 1, 1, 0, 1, 0, 1, 1, 1, 1, 1, 0, 1, 1, 1, 0, 1, 0, 1, 1, 1, 0, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 0, 1, 0, 1, 1, 1, 1, 1, 0, 1, 1, 1, 0, 1, 0, 1, 1, 1, 1, 1, 0, 1, 1, 1, 0, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 0, 1, 0, 1, 1
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| a(n) = signum(A066246(n)), where signum = A057427. For n > 1: a(n) = 1 - A010051(n) = A005171(n).
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LINKS
| Index entries for characteristic functions
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FORMULA
| a(n)={[(n+1)-(n-1)!^2] mod n}, with n>=1 - Paolo P. Lava (paoloplava(AT)gmail.com), Jan 29 2008
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MAPLE
| P:=proc(n) local i; for i from 1 by 1 to n do print(((i+1)-(i-1)!^2) mod i); od; end: P(100); - Paolo P. Lava (paoloplava(AT)gmail.com), Jan 29 2008
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MATHEMATICA
| A066247[n_]:=1-Boole[PrimeQ[n]]-KroneckerDelta[n, 1] [From Enrique Perez Herrero (psychgeometry(AT)gmail.com), Oct 13 2010]
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PROG
| (PARI) a(n)=!isprime(n)&&n>1 \\ Charles R Greathouse IV, Aug 21 2011
(Haskell)
a066247 1 = 0
a066247 n = 1 - a010051 n -- Reinhard Zumkeller, Feb 04 2012
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CROSSREFS
| Cf. A002808, A010051, A005171.
Sequence in context: A174898 A099618 A106002 * A151774 A095792 A169675
Adjacent sequences: A066244 A066245 A066246 * A066248 A066249 A066250
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KEYWORD
| nonn,easy,changed
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AUTHOR
| Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Dec 09 2001
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