1,1

Column 4 of A250387.

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

Empirical: a(n) = 2*a(n-1) +7*a(n-2) -7*a(n-3) +31*a(n-4) +27*a(n-5) -237*a(n-6) -42*a(n-7) +109*a(n-8) -809*a(n-9) +976*a(n-10) +2527*a(n-11) -1891*a(n-12) -83*a(n-13) +2938*a(n-14) -3839*a(n-15) -1155*a(n-16) +1894*a(n-17) -2913*a(n-18) +471*a(n-19) +2319*a(n-20) -198*a(n-21) +36*a(n-22) -216*a(n-24).

Empirical g.f.: 2*x*(210 + 360*x - 106*x^2 + 1137*x^3 - 2269*x^4 - 13879*x^5 - 1808*x^6 + 386*x^7 - 22089*x^8 + 87395*x^9 + 113109*x^10 - 104339*x^11 + 25652*x^12 + 99193*x^13 - 238490*x^14 - 38645*x^15 + 71125*x^16 - 154383*x^17 + 67320*x^18 + 134124*x^19 - 12168*x^20 + 864*x^21 - 3888*x^22 - 12960*x^23) / (1 - 2*x - 7*x^2 + 7*x^3 - 31*x^4 - 27*x^5 + 237*x^6 + 42*x^7 - 109*x^8 + 809*x^9 - 976*x^10 - 2527*x^11 + 1891*x^12 + 83*x^13 - 2938*x^14 + 3839*x^15 + 1155*x^16 - 1894*x^17 + 2913*x^18 - 471*x^19 - 2319*x^20 + 198*x^21 - 36*x^22 + 216*x^24). - Colin Barker, Aug 20 2017

Some solutions for n=5:

..2....4....3....4....2....4....3....0....4....4....4....0....1....0....0....4

..3....0....1....3....4....4....2....1....0....1....1....2....4....4....2....3

..4....3....0....1....3....2....1....0....4....4....4....3....0....2....4....4

..4....1....3....4....2....3....4....3....2....2....0....1....2....4....1....2

..0....4....0....1....0....1....0....3....3....0....3....3....0....1....3....0

..1....1....2....2....0....4....3....0....0....4....4....2....4....0....0....3

..2....2....3....0....2....0....2....0....0....4....4....4....0....3....3....1

..4....0....3....0....3....4....4....4....3....2....0....2....1....2....2....2

Sequence in context: A281210 A235233 A251084 * A145678 A160372 A171259

Adjacent sequences: A250380 A250381 A250382 * A250384 A250385 A250386

R. H. Hardin, Nov 20 2014

approved