61852domain: NAppears in sequencesG.f. is the polynomial (1-x^3) * (1-x^6) * (1-x^9) * (1-x^12) * (1-x^15) * (1-x^18) * (1-x^21) / (1-x)^7.at n=18A162595Number of arrays of 4 integers in -n..n with sum zero and adjacent elements differing in absolute value.at n=22A202964