A156870 Number of nondecreasing sequences of 2n positive integers with reciprocals adding up to n (1 <= n).

1, 4, 18, 168, 3648, 298165, 159628076

Offset: 1

Author

Jens Voß, Feb 17 2009

Keywords

• more
• nonn

Comments

Conjecture: A156869(2n + m, n + m) = a(n) if and only if m >= 0.

Examples

			For n = 2, the a(2) = 4 sequences are (1, 2, 3, 6), (1, 2, 4, 4), (1, 3, 3, 3) and (2, 2, 2, 2) because 1/1 + 1/2 + 1/3 + 1/6 = 1/1 + 1/2 + 1/4 + 1/4 = 1/1 + 1/3 + 1/3 + 1/3 = 1/2 + 1/2 + 1/2 + 1/2 = 2.
		

Crossrefs

a(n) = A156869(2n, n).

Extensions

a(6) from M. F. Hasler, Feb 21 2009

a(7) from Max Alekseyev, Jan 04 2017