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%I #18 Mar 05 2021 03:29:44
%S 0,1,1,2,2,2,1,2,2,2,3,2,2,3,2,2,2,3,3,3,2,3,2,2,2,2,3,2,2,2,3,3,2,3,
%T 2,3,3,2,2,2,2,3,3,2,2,3,4,3,2,3,2,3,3,2,1,2,2,3,3,3,3,2,3,3,3,2,4,3,
%U 2,3,2,2,3,3,3,2,2,3,2,3,3,4,3,2,3,3,2,3,3,4,2,2,2,3,3
%N Number of distinct primes dividing p-1, where p = n-th prime.
%C This is omega(p-1), i.e. A001221(A006093(n)). For Omega(p-1) = A001222(A006093(n)), see A023508. - _Lekraj Beedassy_, Oct 08 2004
%C Primes counted without multiplicity. - _Harvey P. Dale_, May 05 2018
%D N. P. Ryzhova, Asymptotic formulae in a binary problem of shifted prime numbers (in Russian), Additive problems of number theory, Interuniv. Collect. Sci. Works, Kujbyshev 1985 (1985), pp. 25-31.
%H T. D. Noe, <a href="/A008334/b008334.txt">Table of n, a(n) for n=1..10000</a>
%F Sum_{k=1..n} a(k) ~ n*log(log(n))/log(n) + O(n/log(n)) (Ryzhova, 1985). - _Amiram Eldar_, Mar 05 2021
%p for i from 1 to 500 do if isprime(i) then print(nops(factorset(i-1))); fi; od;
%t PrimeNu[#]&/@(Prime[Range[100]]-1) (* _Harvey P. Dale_, May 05 2018 *)
%Y Cf. A001221, A001222, A006093, A023508.
%K nonn
%O 1,4
%A _N. J. A. Sloane_.
%E Definition clarified by _Harvey P. Dale_, May 05 2018
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