1,2

a(n; 1,2) = a(n; 3,2) where S(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.

Same as number of strings over Z_4 of length n with trace 3 and subtrace 2.

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, A073955, A068777, A068786, A068778, A068788, A068789, A073962.

Sequence in context: A147919 A150029 A068787 this_sequence A006820 A131385 A027742

Adjacent sequences: A073956 A073957 A073958 this_sequence A073960 A073961 A073962

easy,nonn

Frank Ruskey, 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