%I A001631 M1081 N0410
%S A001631 0,0,1,0,1,2,4,7,14,27,52,100,193,372,717,1382,2664,5135,9898,19079,
%T A001631 36776,70888,136641,263384,507689,978602,1886316,3635991,7008598,
%U A001631 13509507,26040412,50194508,96753025,186497452,359485397,692930382
%N A001631 Tetranacci numbers: a(n) = a(n-1) + a(n-2) + a(n-3) +a(n-4).
%D A001631 W. C. Lynch, The t-Fibonacci numbers and polyphase sorting, Fib. Quart., 
               8 (1970), pp. 6ff.
%D A001631 N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 
               (includes this sequence).
%D A001631 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%H A001631 S. Plouffe, <a href="http://www.lacim.uqam.ca/%7Eplouffe/articles/MasterThesis.pdf">
               Approximations de S\'{e}ries G\'{e}n\'{e}ratrices et Quelques Conjectures</
               a>, Dissertation, Universit\'{e} du Qu\'{e}bec \`{a} Montr\'{e}al, 
               1992.
%H A001631 S. Plouffe, <a href="http://www.lacim.uqam.ca/%7Eplouffe/articles/FonctionsGeneratrices.pdf">
               1031 Generating Functions and Conjectures</a>, Universit\'{e} du 
               Qu\'{e}bec \`{a} Montr\'{e}al, 1992.
%p A001631 A001631:=(-1+z)/(-1+z+z**2+z**3+z**4); [Conjectured by S. Plouffe in 
               his 1992 dissertation.]
%p A001631 (Maple) a := n -> (Matrix([[0,-1,2,-1]]). Matrix(4, (i,j)-> if (i=j-1) 
               or j=1 then 1 else 0 fi)^n)[1,1] ; seq (a(n), n=0..35); [From Alois 
               P. Heinz (heinz(AT)hs-heilbronn.de), Aug 01 2008]
%Y A001631 First differences of A000078.
%Y A001631 Sequence in context: A005594 A123196 A079968 this_sequence A108758 A018085 
               A167751
%Y A001631 Adjacent sequences: A001628 A001629 A001630 this_sequence A001632 A001633 
               A001634
%K A001631 nonn,easy
%O A001631 0,6
%A A001631 N. J. A. Sloane (njas(AT)research.att.com).
%E A001631 More terms from Larry Reeves (larryr(AT)acm.org), Jul 31 2000