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 A068786 S(n; 1,0) = S(n; 3,0) 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. 9
 1, 2, 6, 16, 40, 192, 896, 4096, 17536, 69632, 270336, 1048576, 4126720, 16515072, 66584576, 268435456, 1077968896, 4311744512, 17213423616, 68719476736, 274608947200, 1098437885952, 4395899027456, 17592186044416, 70385932435456, 281543696187392 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Max Alekseyev, PARI/GP scripts for miscellaneous math problems F. Ruskey, 4-ary strings with given trace and subtrace. FORMULA S(n; t, s) = S(n-1; t, s) + S(n-1; t+3, s+3t+1) + S(n-1; t+2, s+2t) + S(n-1; t+1, s+t+1). Empirical g.f.: x*(1-6*x+14*x^2-16*x^3+8*x^4-32*x^5+32*x^6) / ((1-4*x)*(1-4*x+8*x^2)*(1+16*x^4)). - Colin Barker, Feb 21 2016 CROSSREFS Cf. A068620, A068711, A068774, A068777, A068778, A068787, A068788, A068789, A068790. Sequence in context: A018021 A215340 A074405 * A276359 A158920 A263592 Adjacent sequences:  A068783 A068784 A068785 * A068787 A068788 A068789 KEYWORD nonn,base AUTHOR Frank Ruskey, Mar 29 2002 EXTENSIONS Terms a(11) onward from Max Alekseyev, Apr 09 2013 STATUS approved

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Last modified January 23 22:26 EST 2019. Contains 319404 sequences. (Running on oeis4.)