1,2

a(n; 0,0) 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.

a(3;0,0)=4 since the four 4-ary strings of trace 0, subtrace 0 and length 3 are { 000, 022, 202, 220 }.

Cf. A068711, A073955, A068777, A068786, A068778, A073959, A068788, A068789, A073962.

Sequence in context: A058816 A018446 A068620 this_sequence A094333 A018473 A004094

Adjacent sequences: A073950 A073951 A073952 this_sequence A073954 A073955 A073956

easy,nonn

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

Edited by njas at the suggestion of Andrew Plewe, May 19 2007