A225347 Number of 7Xn -1,1 arrays such that the sum over i=1..7,j=1..n of i*x(i,j) is zero, the sum of x(i,j) is zero, and rows are nondecreasing (number of ways to distribute n-across galley oarsmen left-right at 7 fore-aft positions so that there are no turning moments on the ship).

0, 33, 0, 395, 0, 2073, 0, 7261, 0, 19709, 0, 45385, 0, 92673, 0, 173189, 0, 301799, 0, 497661, 0, 783969, 0, 1189311, 0, 1747059, 0, 2497109, 0, 3484867, 0, 4763439, 0, 6392095, 0, 8439027, 0, 10979255, 0, 14097919, 0, 17887629, 0, 22452391, 0

Offset

1,2

Comments

Row 7 of A225345

Links

R. H. Hardin, Table of n, a(n) for n = 1..210

Formula

Empirical: a(n) = a(n-2) +a(n-4) -a(n-10) -2*a(n-14) +a(n-18) +a(n-20) +a(n-22) +a(n-24) -2*a(n-28) -a(n-32) +a(n-38) +a(n-40) -a(n-42)

Example

Some solutions for n=4
.-1.-1..1..1...-1.-1.-1..1...-1.-1..1..1...-1.-1.-1.-1...-1.-1..1..1
.-1.-1..1..1....1..1..1..1...-1.-1..1..1...-1..1..1..1...-1.-1.-1.-1
.-1.-1.-1..1...-1.-1..1..1...-1.-1..1..1...-1..1..1..1...-1..1..1..1
.-1..1..1..1...-1.-1..1..1....1..1..1..1....1..1..1..1....1..1..1..1
.-1..1..1..1...-1.-1.-1..1...-1.-1.-1.-1...-1.-1.-1.-1...-1.-1.-1..1
.-1.-1.-1..1...-1.-1.-1.-1...-1.-1.-1.-1...-1..1..1..1....1..1..1..1
.-1.-1..1..1....1..1..1..1....1..1..1..1...-1.-1.-1..1...-1.-1.-1.-1

Crossrefs

Sequence in context: A351751 A123238 A372394 * A218116 A279364 A308408

Adjacent sequences: A225344 A225345 A225346 * A225348 A225349 A225350

Keyword

nonn

Author

R. H. Hardin, May 05 2013

Status

approved