OFFSET
0,2
REFERENCES
S. Wolfram, A New Kind of Science, Wolfram Media, 2002; p. 55.
LINKS
Robert Price, Table of n, a(n) for n = 0..1000
Eric Weisstein's World of Mathematics, Elementary Cellular Automaton
S. Wolfram, A New Kind of Science
FORMULA
Conjectures from Colin Barker, Jan 10 2016 and Apr 19 2019: (Start)
a(n) = 3/2+(7*(-1)^n)/2+n-(-1)^n*n for n>2.
a(n) = 2*a(n-2)-a(n-4) for n>6.
G.f.: (1+2*x+2*x^4+2*x^5-3*x^6) / ((1-x)^2*(1+x)^2).
(End)
MATHEMATICA
rule=91; rows=20; ca=CellularAutomaton[rule, {{1}, 0}, rows-1, {All, All}]; (* Start with single black cell *) catri=Table[Take[ca[[k]], {rows-k+1, rows+k-1}], {k, 1, rows}]; (* Truncated list of each row *) Table[Total[catri[[k]]], {k, 1, rows}] (* Number of Black cells in stage n *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Robert Price, Jan 09 2016
STATUS
approved