Number of n X 2 -1,1 arrays such that the sum over i=1..n, j=1..2 of i*x(i,j) is zero, the sum of x(i,j) is zero, and rows are nondecreasing (number of ways to distribute 2-across galley oarsmen left-right at n fore-aft positions so that there are no turning moments on the ship).
A225338
Number of n X 2 -1,1 arrays such that the sum over i=1..n, j=1..2 of i*x(i,j) is zero, the sum of x(i,j) is zero, and rows are nondecreasing (number of ways to distribute 2-across galley oarsmen left-right at n fore-aft positions so that there are no turning moments on the ship).
Terms
- a(0) =1a(1) =1a(2) =1a(3) =1a(4) =3a(5) =7a(6) =15a(7) =33a(8) =77a(9) =181a(10) =443a(11) =1113a(12) =2837a(13) =7283a(14) =18909a(15) =49635a(16) =131427a(17) =350419a(18) =940417a(19) =2538857a(20) =6890577a(21) =18790165a(22) =51462893a(23) =141509487a(24) =390530601a(25) =1081369087a(26) =3003537529a(27) =8366306613a(28) =23366125605a(29) =65420219243
External references
- oeis: A225338