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

Author

R. K. Guy, Nov 19 2002

Keywords

• nonn
• easy
• look

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

Crossrefs

Cf. A006530, A119288, A292269.

Programs

PARI

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

Formula

If p_1 < p_2 < ...

Extensions

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

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