A023524 - OEIS

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A023524

Number of distinct prime divisors of prime(n)*prime(n-1) + 1.

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

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OFFSET

1,4

COMMENTS

This is taking prime(0)=1. - Robert Israel, Dec 22 2015

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

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

Adjacent sequences: A023521 A023522 A023523 * A023525 A023526 A023527

KEYWORD

nonn

AUTHOR

Clark Kimberling

STATUS

approved