209446domain: NAppears in sequencesExpansion of g.f.: 1/(1 - x - 2*x^2 + x^3 + x^4 + 2*x^7 - 5*x^9 + 2*x^11 + x^14 + x^15 - 2*x^16 - x^17 + x^18).at n=26A147622Number of -n..n arrays x(0..3) of 4 elements with zero sum and nonzero first and second differences.at n=33A200456