A076820 Second-largest distinct prime dividing n (or 1 if n is a power of a prime).

1, 1, 1, 1, 1, 2, 1, 1, 1, 2, 1, 2, 1, 2, 3, 1, 1, 2, 1, 2, 3, 2, 1, 2, 1, 2, 1, 2, 1, 3, 1, 1, 3, 2, 5, 2, 1, 2, 3, 2, 1, 3, 1, 2, 3, 2, 1, 2, 1, 2, 3, 2, 1, 2, 5, 2, 3, 2, 1, 3, 1, 2, 3, 1, 5, 3, 1, 2, 3, 5, 1, 2, 1, 2, 3, 2, 7, 3, 1, 2, 1, 2, 1, 3, 5, 2, 3, 2, 1, 3, 7, 2, 3, 2, 5, 2, 1, 2, 3, 2, 1, 3, 1, 2, 5

Offset

1,6

Comments

The 3rd-largest is 1 except 2 at 30, 42, 60, 66, 70, ...

Links

Antti Karttunen, Table of n, a(n) for n = 1..65537

Formula

If p_1 < p_2 < ... <p_{k-1} < p_k are the distinct primes dividing n then a(n) = p_{k-1}.

Prog

(PARI) A076820(n) = { my(o=omega(n)); if(1>=o, 1, factor(n)[o-1, 1]); }; \\ Antti Karttunen, Sep 25 2018

Crossrefs

Cf. A006530, A119288, A292269.

Sequence in context: A337531 A316556 A187279 * A206824 A293810 A356553

Adjacent sequences: A076817 A076818 A076819 * A076821 A076822 A076823

Keyword

nonn,easy,look

Author

R. K. Guy, Nov 19 2002

Extensions

More terms from Jason Earls and John W. Layman, Nov 21 2002

Status

approved