A171435 - OEIS

A171435

Product of odd prime factors < n, with multiplicity.

1, 1, 1, 1, 1, 3, 1, 1, 9, 5, 1, 3, 1, 7, 15, 1, 1, 9, 1, 5, 21, 11, 1, 3, 25, 13, 27, 7, 1, 15, 1, 1, 33, 17, 35, 9, 1, 19, 39, 5, 1, 21, 1, 11, 45, 23, 1, 3, 49, 25, 51, 13, 1, 27, 55, 7, 57, 29, 1, 15, 1, 31, 63, 1, 65, 33, 1, 17, 69, 35, 1, 9, 1, 37, 75, 19, 77, 39, 1, 5, 81, 41, 1, 21, 85

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OFFSET

1,6

COMMENTS

In this sequence p < n, but p^k with k>=2 may be equal to n.

a(n) = 1 iff n = 2^k, k >= 0 or n is prime;

1 < a(n) < n iff n is even composite and not a power of 2;

a(n) = n iff n is nonprime (unit or composite) odd.

LINKS

Daniel Forgues, Table of n, a(n) for n=1..100000

FORMULA

If A010051(n) = 1 [when n is a prime], then a(n) = 1, otherwise a(n) = A000265(n). - Antti Karttunen, Mar 27 2022