cp's OEIS Frontend

A061394 Number of distinct prime factors of n-th least prime signature (A025487); also a(n)-th prime is largest prime factor of n-th least prime signature; also a(n)-th primorial number is largest primorial factor of n-th least product of primorial numbers.

%I A061394 #19 Nov 07 2014 12:00:57
%S A061394 0,1,1,2,1,2,1,2,3,1,2,2,3,1,2,2,3,1,2,3,2,4,2,3,1,2,3,2,4,2,3,1,2,3,
%T A061394 2,4,2,3,3,1,3,2,4,2,3,2,4,2,3,3,1,3,2,5,4,2,3,2,4,2,3,3,1,3,2,5,4,2,
%U A061394 3,3,2,4,3,4,2,3,4,3,2,1,3,2,5,4,2,3,3,2,4,3,4,2,5,3,4,3,2,1,3,2,5,4,2,3,3
%N A061394 Number of distinct prime factors of n-th least prime signature (A025487); also a(n)-th prime is largest prime factor of n-th least prime signature; also a(n)-th primorial number is largest primorial factor of n-th least product of primorial numbers.
%C A061394 A002110(a(n)) = A247451(n). - _Reinhard Zumkeller_, Sep 17 2014
%C A061394 Number of parts of the associated prime signature. - _Álvar Ibeas_, Nov 01 2014
%H A061394 Reinhard Zumkeller, <a href="/A061394/b061394.txt">Table of n, a(n) for n = 1..10000</a>
%F A061394 a(n) = A061395(A025487(n)) = A001221(A025487(n)) = A051903(A181822(n)).
%F A061394 A000040(a(n)) = A006530(A025487(n)).
%o A061394 (Haskell)
%o A061394 import Data.List (elemIndex); import Data.Maybe (fromJust)
%o A061394 a061394 = fromJust . (`elemIndex` a002110_list) . a247451
%o A061394 -- _Reinhard Zumkeller_, Sep 17 2014
%o A061394 (PARI) isA025487(n)=my(k=valuation(n, 2), t); n>>=k; forprime(p=3, default(primelimit), t=valuation(n, p); if(t>k, return(0), k=t); if(k, n/=p^k, return(n==1)))
%o A061394 [omega(n) | n <- [1..1000], isA025487(n)]
%o A061394 \\ Or, for older versions:
%o A061394 apply(omega, select(isA025487, [1..1000])) \\ _Charles R Greathouse IV_, Nov 07 2014
%Y A061394 Cf. A002110, A247451, A006530, A061395, A025487, A000040, A051903. A001221 by prime signature.
%K A061394 nonn
%O A061394 1,4
%A A061394 _Henry Bottomley_, Apr 30 2001
%E A061394 Offset updated by _Matthew Vandermast_, Nov 08 2008