OFFSET
0,2
REFERENCES
Stephen Wolfram, A New Kind of Science, Wolfram Media, 2002; p. 55.
LINKS
Robert Price, Table of n, a(n) for n = 0..999
Eric Weisstein's World of Mathematics, Elementary Cellular Automaton
Index entries for linear recurrences with constant coefficients, signature (0,21,0,-84,0,64).
FORMULA
From Colin Barker, Dec 27 2015 and Apr 14 2019: (Start)
a(n) = 21*a(n-2)-84*a(n-4)+64*a(n-6) for n>5.
G.f.: (1+2*x-16*x^2+64*x^3-96*x^5) / ((1-x)*(1+x)*(1-2*x)*(1+2*x)*(1-4*x)*(1+4*x)).
(End)
a(n) = 2*4^n - (8*2^n-1)/3 - 1 for odd n; a(n) = (4*2^n-1)/3 for even. - Karl V. Keller, Jr., Aug 27 2021
MATHEMATICA
rule=13; 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[FromDigits[catri[[k]], 2], {k, 1, rows}] (* Decimal Representation of Rows *)
PROG
(Python) print([2*4**n - (8*2**n-1)//3 - 1 if n%2 else (4*2**n-1)//3 for n in range(50)]) # Karl V. Keller, Jr., Aug 27 2021
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Robert Price, Dec 26 2015
STATUS
approved