1,3

G. C. Greubel, Table of n, a(n) for n = 1..1000

a(n) = omega(prime(n) + prime(n + 1) = A001221(A001043(n)), where omega is the number of distinct prime factors function.

Prime(6) = 13 and prime(7) = 17. 13 + 17 = 30 = 2 * 3 * 5, which has three distinct prime factors, hence a(6) = 3.

Table[PrimeNu[Prime[n] + Prime[n + 1]], {n, 105}] (* Jean-François Alcover, Oct 21 2013 *)

(PARI) A071215(n)=omega(prime(n)+prime(n+1)) \\ M. F. Hasler, Jul 23 2007

Cf. A001043, A001221, A071216.

Sequence in context: A091322 A252229 A318490 * A164024 A145193 A292585

Adjacent sequences: A071212 A071213 A071214 * A071216 A071217 A071218

easy,nonn

Labos Elemer, May 17 2002

approved