A268869 Number of sequences in {1,...,n}^n with longest increasing subsequence of length two.

1, 16, 175, 1771, 17906, 184920, 1958979, 21253375, 235401166, 2653427140, 30356604642, 351714783980, 4119532070980, 48708027030608, 580682498991627, 6973355148949335, 84286653134676230, 1024694093358751200, 12522664845237058050, 153762682169941498170

Offset: 2

Author

Alois P. Heinz, Feb 15 2016

Keywords

• nonn
• easy

Examples

			a(2) = 1: 12.
a(3) = 16: 112, 113, 121, 122, 131, 132, 133, 212, 213, 223, 231, 232, 233, 312, 313, 323.
a(4) = 175: 1112, 1113, 1114, 1121, ..., 4414, 4423, 4424, 4434.
		

Links

• Alois P. Heinz, Table of n, a(n) for n = 2..900

Crossrefs

Column k=2 of A245667.

Cf. A001700, A088218, A239295.

Formula

a(n) = A239295(n) - A088218(n) = A239295(n) - A001700(n-1).