A084717 a(1) = 3 then a(n) = smallest multiple of a(n-1) > a(n-1) such that a(n) - 1 is a prime.

3, 6, 12, 24, 48, 192, 384, 1152, 6912, 27648, 138240, 691200, 3456000, 34560000, 138240000, 414720000, 2073600000, 16588800000, 364953600000, 4744396800000, 66421555200000, 132843110400000, 664215552000000, 3321077760000000, 6642155520000000, 132843110400000000

Offset: 1

Author

Amarnath Murthy, Jun 11 2003

Keywords

• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 1..586

Crossrefs

Cf. A084716, A084718, A036012.

Programs

Mathematica

a[1] = 3; a[n_] := a[n] = Catch[For[k = 2, True, k++, an = k*a[n - 1]; If[PrimeQ[an - 1], Throw[an]]]]; Table[a[n], {n, 1, 22}](* Jean-François Alcover, Nov 27 2012 *)
smp[n_]:=Module[{k=2},While[!PrimeQ[k*n-1],k++];k*n]; NestList[smp,3,30] (* Harvey P. Dale, Jun 03 2015 *)

Extensions

Edited by Don Reble, Jun 19 2003