A385209 Least k such that A086369(k) = n.

1, 2, 3, 4, 9, 6, 15, 16, 81, 12, 45, 64, 729, 24, 105, 36, 225, 48, 405, 1024, 59049, 60, 315, 4096, 531441, 192, 3645, 144, 2025, 120, 945, 65536, 43046721, 180, 1575, 262144, 387420489, 240, 2835, 576, 18225, 3072, 295245, 4194304, 31381059609, 360, 3465, 1296

Offset: 1

Author

Miles Englezou, Jun 21 2025

Keywords

• nonn

Comments

A086369(n) is also the cardinality of the set containing the divisors d of n and those 0 < m < n satisfying m + d = n.

Examples

			a(4) = 4 since 4 is the least k such that A086369(k) = 4.
a(13) = 729 since 729 is the least k such that A086369(k) = 13.
		

Crossrefs

Cf. A086369, A385202.

Programs

PARI

a(n,k) = my(f); (f(n) = if(n%2==1, 1+2*sumdiv(n,d,d
				

Formula

a(2*p-1) = 3^(p-1) for prime p. - Jinyuan Wang, Jun 30 2025

Extensions

a(45)-a(48) from Jinyuan Wang, Jun 30 2025