-130320domain: ZAppears in sequencesa(n) = 1 - n^4.at n=19A024002a(n) = Sum_{d|n, d==1 mod 4} d^4 - Sum_{d|n, d==3 mod 4} d^4.at n=18A050456a(n) = Sum_{d|n, d==1 mod 4} d^4 - Sum_{d|n, d==3 mod 4} d^4.at n=37A050456Jordan function J_{-4} multiplied by n^4.at n=18A189922