A102401 a(n) is the index of the permutation of order n having the least sum of pairwise products as given by A026035.

0, 2, 14, 80, 512, 3776, 31376, 290456, 2970296, 33276536, 405440216, 5338909736, 75572075816, 1144441325096, 18464406889256, 316212570391976, 5729159765566376

Offset: 2

Author

Eugene McDonnell (eemcd(AT)mac.com), Feb 22 2005

Keywords

• easy
• nonn

Comments

A026035 gives the minimum sum of products for permutations and was used to validate the results above. There is a companion index for the permutations that are the reversals of those indexed here. A formula would be very welcome.

Examples

			In the permutation table of order 7 the first instance of a row having the least sum of overlapping pairwise products can be found empirically to be:
6 2 4 3 5 1 7
and this is found at index 3776. Its products are
12 8 12 15 5 7
and sum is 59; a(7) of A026035 is 59. This allows us to give a(7) as 3776.