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

Author

Labos Elemer, Nov 26 2003

Keywords

• nonn

Crossrefs

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

Cf. A090093, A090094, A090095.

Programs

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 *)

Formula

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