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A023524
Number of distinct prime divisors of prime(n)*prime(n-1) + 1.
3
1, 1, 1, 2, 3, 2, 3, 2, 3, 2, 3, 3, 4, 3, 3, 3, 3, 3, 3, 4, 2, 3, 3, 2, 3, 4, 3, 4, 2, 3, 4, 4, 3, 3, 3, 3, 2, 3, 4, 3, 3, 3, 4, 2, 3, 3, 5, 3, 5, 3, 3, 2, 3, 3, 2, 4, 3, 3, 3, 3, 3, 4, 3, 3, 3, 4, 3, 3, 4, 3, 3, 4, 4, 3, 3, 4, 4, 4, 4, 6, 3, 4, 3, 2, 2, 3, 2
OFFSET
1,4
COMMENTS
This is taking prime(0)=1. - Robert Israel, Dec 22 2015
LINKS
MAPLE
1, seq(nops(numtheory:-factorset(ithprime(n)*ithprime(n-1)+1)), n=2..100); # Robert Israel, Dec 22 2015
MATHEMATICA
Prepend[Table[PrimeNu[Prime@ n Prime[n - 1] + 1], {n, 2, 80}], 1] (* Michael De Vlieger, Dec 22 2015 *)
PROG
(PARI) a(n) = if (n==1, 1, omega(prime(n)*prime(n-1) + 1)); \\ Michel Marcus, Dec 22 2015
(Magma) [#PrimeDivisors((NthPrime(n)*(NthPrime(n-1))+1)): n in [1..100]]; // Vincenzo Librandi, Dec 23 2015
CROSSREFS
Sequence in context: A171465 A178620 A342866 * A068639 A074070 A304097
KEYWORD
nonn
STATUS
approved