A245908 The number of distinct prime factors of prime(n)^2-1.

1, 1, 2, 2, 3, 3, 2, 3, 3, 4, 3, 3, 4, 4, 3, 3, 4, 4, 4, 4, 3, 4, 4, 4, 3, 4, 4, 3, 4, 4, 3, 5, 4, 5, 4, 4, 4, 3, 4, 4, 4, 5, 4, 3, 4, 4, 5, 4, 4, 5, 4, 5, 4, 4, 3, 4, 4, 4, 4, 5, 4, 4, 5, 5, 4, 4, 5, 4, 4, 5, 4, 4, 4, 5, 5, 3, 5, 4, 4, 5

Offset: 1

Author

R. J. Mathar, Aug 05 2014

Keywords

• nonn

Links

• Jens Kruse Andersen, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A008334, A008335, A082863.

Programs

Magma

[#PrimeDivisors(NthPrime(n)^2 -1): n in [1..100]]; // Vincenzo Librandi, Apr 27 2019

Maple

A245908 := proc(n)
    A082863(ithprime(n)) ;
end proc:

Mathematica

Table[PrimeNu[Prime[n]^2 - 1], {n, 100}] (* Wesley Ivan Hurt, Aug 05 2014 *)

PARI

vector(100, n, omega(prime(n)^2-1)) \\ Derek Orr, Aug 05 2014

Formula

a(n) = A082863(prime(n)).

a(n) = A008334(n) + A008335(n) - 1, if n>1.