Number of unordered sets a, b, c, d of distinct integers from 1..n such that a+b+c+d = 0 (mod n).

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =1a(5) =3a(6) =5a(7) =9a(8) =14a(9) =22a(10) =30a(11) =42a(12) =55a(13) =73a(14) =91a(15) =115a(16) =140a(17) =172a(18) =204a(19) =244a(20) =285a(21) =335a(22) =385a(23) =445a(24) =506a(25) =578a(26) =650a(27) =734a(28) =819a(29) =917