A171435 - OEIS

%I #6 Mar 27 2022 23:31:14

%S 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,

%T 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,

%U 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

%N Product of odd prime factors < n, with multiplicity.

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

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

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

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

%H Daniel Forgues, <a href="/A171435/b171435.txt">Table of n, a(n) for n=1..100000</a>

%F If A010051(n) = 1 [when n is a prime], then a(n) = 1, otherwise a(n) = A000265(n). - _Antti Karttunen_, Mar 27 2022

%o (PARI) A171435(n) = if(isprime(n), 1, n>>valuation(n,2)); \\ _Antti Karttunen_, Mar 27 2022

%Y Cf. A171487, A000265, A010051.

%K nonn

%O 1,6

%A _Daniel Forgues_, Dec 09 2009

%E Edited by _Daniel Forgues_, Dec 10 2009