1,3

54% of a(n) for n=1 to 1755 are < 0.1*n^2.

Pierre CAMI, Table of n, a(n) for n = 1..1755

lon[n_]:=Module[{k=1, n2=3*2^n}, While[!PrimeQ[k*n2-1]||!PrimeQ[k*n2+1], k= k+2]; k]; Array[lon, 60] (* Harvey P. Dale, Nov 27 2015 *)

Cf. A210651.

Sequence in context: A154143 A101611 A268409 * A282141 A318321 A279510

Adjacent sequences: A182027 A182028 A182029 * A182031 A182032 A182033

nonn

Pierre CAMI, Apr 07 2012

approved