A085710 Smallest k such that kn+1 is a semiprime.

3, 4, 1, 2, 1, 4, 2, 1, 1, 2, 3, 2, 1, 1, 3, 2, 2, 3, 2, 1, 1, 5, 4, 1, 1, 7, 2, 2, 5, 3, 3, 1, 1, 1, 3, 4, 1, 1, 3, 3, 5, 2, 2, 3, 1, 2, 2, 1, 6, 1, 4, 4, 4, 1, 2, 1, 1, 5, 2, 2, 1, 3, 4, 1, 5, 2, 3, 1, 5, 2, 2, 2, 1, 5, 3, 1, 2, 3, 2, 2, 1, 3, 10, 1, 1, 1, 3, 2, 5, 1, 2, 1, 1, 1, 4, 3, 6, 3, 3, 2, 2, 2, 4, 2, 1

Offset

1,1

Comments

Conjecture: for every n > 2 there exists a number k < n such that n*k + 1 is a semiprime.

Links

T. D. Noe, Table of n, a(n) for n=1..1000

Mathematica

sk[n_]:=Module[{k=1}, While[PrimeOmega[k*n+1]!=2, k++]; k]; Array[sk, 120] (* Harvey P. Dale, Mar 12 2019 *)

Crossrefs

Cf. A001358.

Sequence in context: A204999 A373828 A294731 * A248004 A106650 A076942

Adjacent sequences: A085707 A085708 A085709 * A085711 A085712 A085713

Keyword

easy,nonn

Author

Jason Earls, Jul 19 2003

Status

approved