A090093 a(n) is the smallest composite number coprime to n, n+1, n+2, n+3.

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

Offset: 1

Author

Labos Elemer, Nov 26 2003

Keywords

• nonn

Crossrefs

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

Cf. A090092, 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]&&Equal[s3, 1]&&!PrimeQ[n]&&!Equal[n, 1] &&Equal[fla, 1], m=m+1;Print[n];fla=0], {n, 1, 1000}], {k, 1, 256}]
With[{compnos=Complement[Range[2,500],Prime[Range[PrimePi[500]]]]}, Table[ First[Select[compnos,And@@CoprimeQ[#,n+Range[0,3]]&]],{n,70}]] (* Harvey P. Dale, Aug 10 2011 *)

Formula

a(n) = A053672(n)^2.