A071215 Number of distinct prime factors of sum of 2 successive primes.

1, 1, 2, 2, 2, 3, 2, 3, 2, 3, 2, 3, 3, 3, 2, 2, 3, 1, 3, 2, 2, 2, 2, 3, 3, 3, 4, 2, 3, 3, 3, 2, 3, 2, 3, 3, 2, 4, 3, 2, 3, 3, 2, 4, 3, 3, 3, 3, 3, 4, 2, 3, 3, 2, 3, 3, 3, 2, 3, 3, 2, 3, 3, 3, 4, 2, 2, 3, 3, 3, 2, 3, 3, 2, 3, 2, 3, 4, 3, 3, 4, 3, 2, 2, 3, 2, 3, 3, 4, 4, 3, 4, 3, 4, 3, 3, 3, 3, 3, 2, 3, 3, 2, 4, 3

Offset

1,3

Links

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

Formula

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

Example

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

Mathematica

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

Prog

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

Crossrefs

Cf. A001043, A001221, A071216.

Sequence in context: A091322 A252229 A318490 * A164024 A145193 A292585

Adjacent sequences: A071212 A071213 A071214 * A071216 A071217 A071218

Keyword

easy,nonn

Author

Labos Elemer, May 17 2002

Status

approved