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A071215 Number of distinct prime factors of sum of 2 successive primes. 5
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 (list; graph; refs; listen; history; text; internal format)
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-Fran├žois 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

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Last modified March 24 06:56 EDT 2019. Contains 321444 sequences. (Running on oeis4.)