login
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
OFFSET
1,3
LINKS
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
KEYWORD
easy,nonn
AUTHOR
Labos Elemer, May 17 2002
STATUS
approved