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A089090
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a(n) is the smallest composite number coprime to n.
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0
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4, 9, 4, 9, 4, 25, 4, 9, 4, 9, 4, 25, 4, 9, 4, 9, 4, 25, 4, 9, 4, 9, 4, 25, 4, 9, 4, 9, 4, 49, 4, 9, 4, 9, 4, 25, 4, 9, 4, 9, 4, 25, 4, 9, 4, 9, 4, 25, 4, 9, 4, 9, 4, 25, 4, 9, 4, 9, 4, 49, 4, 9, 4, 9, 4, 25, 4, 9, 4, 9, 4, 25, 4, 9, 4, 9, 4, 25, 4, 9, 4, 9, 4, 25, 4, 9, 4, 9, 4, 49, 4, 9, 4, 9, 4, 25, 4
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,1
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FORMULA
| a[n]=A053669[n]^2
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EXAMPLE
| n=30: below 30 coprimes to 30 phi[30]=8 numbers are relevant but each 1 or primes; so a[n]>30; the first suitable number is a[30]=49; If n is the n-th primorial, then a[n]=p(n+1)^2.
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MATHEMATICA
| m=0; Table[fla=1; Do[s=GCD[n, k]; If[Equal[s, 1]&&!PrimeQ[n]&&!Equal[n, 1]&& Equal[fla, 1], m=m+1; Print[n]; fla=0], {n, 1, 130}], {k, 1, 256}]
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CROSSREFS
| Cf. A053669, A007978, A053670-A053674, A090091-A090093.
Sequence in context: A141653 A071793 A010714 * A204919 A113484 A061767
Adjacent sequences: A089087 A089088 A089089 * A089091 A089092 A089093
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KEYWORD
| easy,nonn
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AUTHOR
| Labos E. (labos(AT)ana.sote.hu), Nov 26 2003
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