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Number of distinct primes dividing p+1 as p runs through the primes.
3

%I #15 Sep 10 2024 08:44:39

%S 1,1,2,1,2,2,2,2,2,3,1,2,3,2,2,2,3,2,2,2,2,2,3,3,2,3,2,2,3,3,1,3,3,3,

%T 3,2,2,2,3,3,3,3,2,2,3,2,2,2,3,3,3,3,2,3,3,3,3,2,2,3,2,3,3,3,2,3,2,2,

%U 3,3,3,3,2,3,3,2,4,2,3,3,4,2,2,3,3,3,3,2,4,2,3,3,2,3,2

%N Number of distinct primes dividing p+1 as p runs through the primes.

%H T. D. Noe, <a href="/A008335/b008335.txt">Table of n, a(n) for n=1..10000</a>

%F a(n) = A001221(A008864(n)). - _Michel Marcus_, Mar 29 2016

%p for i from 1 to 500 do if isprime(i) then print(nops(factorset(i+1))); fi; od;

%t a[n_] := PrimeNu[Prime[n]+1]; Array[a, 100] (* _Amiram Eldar_, Sep 10 2024 *)

%o (PARI) a(n) = omega(prime(n)+1); \\ _Michel Marcus_, Mar 29 2016

%Y Cf. A001221, A008864, A023514.

%K nonn,easy

%O 1,3

%A _N. J. A. Sloane_.