A090092 a(n) is the smallest composite number coprime to n, n+1 and n+2.

25, 25, 49, 49, 121, 25, 25, 49, 49, 49, 25, 25, 121, 121, 49, 25, 25, 49, 121, 169, 25, 25, 49, 49, 49, 25, 25, 121, 49, 49, 25, 25, 169, 121, 121, 25, 25, 49, 49, 121, 25, 25, 49, 49, 49, 25, 25, 121, 121, 49, 25, 25, 49, 169, 169, 25, 25, 49, 49, 49, 25, 25, 121, 49, 49, 25

Offset

1,1

Links

Table of n, a(n) for n=1..66.

Formula

a(n) = A053671(n)^2.

Mathematica

m=0; Table[fla=1; Do[s=GCD[n, k]; s1=GCD[n, k+1]; s2=GCD[n, k+2]; s3=GCD[n, k+3]; If[Equal[s, 1]&&Equal[s1, 1]&&Equal[s2, 1] &&!PrimeQ[n]&&!Equal[n, 1] &&Equal[fla, 1], m=m+1; Print[n]; fla=0], {n, 1, 1000}], {k, 1, 256}]
nn=200; With[{c=Complement[Range[2, nn], Prime[Range[PrimePi[nn]]]]}, Flatten[ Table[ Select[c, And@@Thread[CoprimeQ[{n, n+1, n+2}, #]]&, 1], {n, nn}]]](* Harvey P. Dale, Sep 28 2013 *)

Crossrefs

Cf. A053669, A053670, A053671, A053672, A053673, A053674.

Cf. A090093, A090094, A090095.

Sequence in context: A010864 A283710 A247650 * A323522 A040601 A022359

Adjacent sequences: A090089 A090090 A090091 * A090093 A090094 A090095

Keyword

nonn

Author

Labos Elemer, Nov 26 2003

Status

approved