OFFSET
1,2
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
FORMULA
From Robert Israel, Jun 06 2016: (Start)
a(3n+3) = 9a(n)+4.
otherwise a(3n+2) = 9a(n)+1 and a(3n+4) = 9a(n)+7.
G.f. satisfies g(x) = 9(x^2+x^3+x^4)g(x^3) + (x+2x^2+4x^3+6x^4-x^5)/(1-x^3) + ((2+2x)/(x+x^2+x^3)) Sum_{k>=1}(x^(2*3^k)-x^(4*3^k)).
(End)
MAPLE
N:= 1000: # to get a(1) to a(N)
K:= ceil((N-4)/3):
Dmax:= ilog[3](ceil(K/2+1)):
A:= Vector(3*K+4):
A[1..4]:= <1, 2, 4, 7>:
for d from 0 to Dmax do
for k from 2*3^d-1 to min(4*3^d-2, K) do
A[3*k+2]:= 9*A[k]+3;
A[3*k+3]:= 9*A[k]+4;
A[3*k+4]:= 9*A[k]+5
od:
for k from 4*3^d-1 to min(2*3^(d+1)-2, K) do
A[3*k+2]:= 9*A[k]+1;
A[3*k+3]:= 9*A[k]+4;
A[3*k+4]:= 9*A[k]+7
od:
od:
seq(A[i], i=1..N); # Robert Israel, Jun 06 2016
CROSSREFS
KEYWORD
nonn,base
AUTHOR
EXTENSIONS
Name corrected by Robert Israel, Jun 06 2016
STATUS
approved