A166780 Number of nX2 1..7 arrays containing at least one of each value, all equal values connected, and rows considered as a single number in nondecreasing order.

0, 0, 0, 2730, 33586, 206864, 889743, 3049239, 8915556, 23162008, 54891826, 120841344, 250363790, 492955632

Offset

1,4

Links

Table of n, a(n) for n=1..14.

Formula

From G. C. Greubel, May 26 2016: (Start)

Empirical a(n) = (32/(12)!)*(n-1)*(n-2)*(n-3)*(2*n^9 + 156*n^8 + 6546*n^7 + 168582 n^6 + 2509143*n^5 + 18010344*n^4 + 22858999*n^3 - 183485232*n^2 + 74391660*n - 2494800).

Empirical G.f.: x^4*(x^9 + 416*x^8 - 2091*x^7 + 1182*x^6 + 12779*x^5 - 35674*x^4 + 39439*x^3 - 16814*x^2 - 1904*x + 2730)/(1-x)^13. (End)

Example

Some solutions for n=4
...1.7...2.5...1.4...3.1...1.3...5.2...3.1...2.4...2.4...3.5...1.2...1.6...3.1
...2.2...3.4...6.3...3.5...4.6...6.1...3.7...2.5...3.7...4.1...6.3...3.2...3.6
...5.3...7.1...6.5...4.2...5.2...6.3...4.2...3.7...5.7...7.2...7.4...3.7...4.7
...6.4...7.6...7.2...6.7...7.2...7.4...6.5...6.1...6.1...7.6...7.5...5.4...5.2
------
...1.3...1.3...1.2...1.2...1.3...2.7...1.4...2.1...2.1...1.1...2.7...2.7...5.1
...4.5...2.7...4.3...5.3...2.5...3.4...1.6...3.4...3.4...2.3...3.4...3.5...5.3
...6.2...4.4...4.5...6.4...4.6...5.1...2.7...5.6...3.5...5.6...3.5...4.4...6.4
...6.7...6.5...7.6...6.7...7.7...5.6...3.5...7.7...7.6...7.4...6.1...6.1...7.2

Crossrefs

Sequence in context: A031608 A350047 A043579 * A068305 A031812 A308800

Adjacent sequences: A166777 A166778 A166779 * A166781 A166782 A166783

Keyword

nonn,more

Author

R. H. Hardin, Oct 21 2009

Status

approved