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.

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, 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, 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

Offset

1,4

Comments

A002110(a(n)) = A247451(n). - Reinhard Zumkeller, Sep 17 2014

Number of parts of the associated prime signature. - Álvar Ibeas, Nov 01 2014

Links

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Formula

a(n) = A061395(A025487(n)) = A001221(A025487(n)) = A051903(A181822(n)).

A000040(a(n)) = A006530(A025487(n)).

Prog

(Haskell)
import Data.List (elemIndex); import Data.Maybe (fromJust)
a061394 = fromJust . (`elemIndex` a002110_list) . a247451
-- Reinhard Zumkeller, Sep 17 2014
(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)))
[omega(n) | n <- [1..1000], isA025487(n)]
\\ Or, for older versions:
apply(omega, select(isA025487, [1..1000])) \\ Charles R Greathouse IV, Nov 07 2014

Crossrefs

Cf. A002110, A247451, A006530, A061395, A025487, A000040, A051903. A001221 by prime signature.

Sequence in context: A105265 A351468 A193360 * A248141 A220694 A136314

Adjacent sequences: A061391 A061392 A061393 * A061395 A061396 A061397

Keyword

nonn

Author

Henry Bottomley, Apr 30 2001

Extensions

Offset updated by Matthew Vandermast, Nov 08 2008

Status

approved