1,4

a(n; 0,2) where a(n; t,s) is the number of length n 4-ary strings whose digits sum to t mod 4 and whose sum of products of all pairs of digits sum to s mod 4.

F. Ruskey, Strings over Z_4 of given Trace and Subtrace

a(n; t, s) = a(n-1; t, s) + a(n-1; t+3, s+3t+1) + a(n-1; t+2, s+2t) + a(n-1; t+1, s+t+1) where t is the trace and s is the subtrace.

Cf. A073953, A068711, A068777, A068786, A068778, A073959, A068788, A068789, A073962.

Sequence in context: A051199 A068774 A068775 this_sequence A158922 A117083 A007987

Adjacent sequences: A073952 A073953 A073954 this_sequence A073956 A073957 A073958

easy,nonn

Frank Ruskey and Nate Kube (fruskey(AT)cs.uvic.ca), Aug 15 2002

Edited by N. J. A. Sloane (njas(AT)research.att.com) at the suggestion of Andrew Plewe, May 20 2007