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

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

Prog

(PARI) A171435(n) = if(isprime(n), 1, n>>valuation(n, 2)); \\ Antti Karttunen, Mar 27 2022

Crossrefs

Cf. A171487, A000265, A010051.

Sequence in context: A142992 A145905 A336859 * A144183 A050153 A294950

Adjacent sequences: A171432 A171433 A171434 * A171436 A171437 A171438

Keyword

nonn

Author

Daniel Forgues, Dec 09 2009

Extensions

Edited by Daniel Forgues, Dec 10 2009

Status

approved