OFFSET
0,3
REFERENCES
Stephen Wolfram, A New Kind of Science, Wolfram Media, 2002; p. 55.
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..500
Eric Weisstein's World of Mathematics, Elementary Cellular Automaton
Index entries for linear recurrences with constant coefficients, signature (0,25,0,-152,0,128).
FORMULA
From Colin Barker, Dec 29 2015 and Apr 15 2019: (Start)
a(n) = 25*a(n-2)-152*a(n-4)+128*a(n-6) for n>5.
G.f.: (1-2*x)*(1+3*x-11*x^2+32*x^3+80*x^4) / ((1-x)*(1+x)*(1-4*x)*(1+4*x)*(1-8*x^2)). (End)
a(n) = 8^(n/2) + (1-(-1)^n)*(2*4^n-8^(n/2)-6*8^((n-1)/2)-1)/2. Therefore: for even n, a(n) = 8^(n/2); otherwise, a(n) = 2*4^n - 6*8^((n-1)/2) - 1. - Bruno Berselli, Dec 29 2015
MATHEMATICA
rule=17; 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
(Sage) [8^(n/2)+(1-(-1)^n)*(2*4^n-8^(n/2)-6*8^((n-1)/2)-1)/2 for n in [0..30]] # Bruno Berselli, Dec 29 2015
(Magma) [IsEven(n) select 8^(n div 2) else 2*4^n-6*8^((n-1) div 2)-1: n in [0..30]]; // Bruno Berselli, Dec 29 2015
(Python) print([2*4**n - 6*8**((n-1)//2) - 1 if n%2 else 8**(n//2) for n in range(50)]) # Karl V. Keller, Jr., Aug 31 2021
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Robert Price, Dec 27 2015
STATUS
approved