OFFSET
1,3
COMMENTS
Also, the number of finite sequences b(1..r) satisfying b(1) = 1 and b(i+1) >= 3*b(i) and b(r) <= n.
EXAMPLE
For n = 10 the 11 sequences enumerated are (1), (1,3), (1,4), (1,5), (1,6), (1,7), (1,8), (1,9), (1,10), (1,3,9), (1,3,10).
MAPLE
a:= proc(n) option remember;
`if`(n<2, n, a(n-1)+a(iquo(n, 3)))
end:
seq(a(n), n=1..75); # Alois P. Heinz, Dec 16 2019
MATHEMATICA
Nest[Append[#1, #1[[-1]] + #1[[Floor[#2/3] ]] ] & @@ {#, Length@ # + 1} &, {1, 1}, 57] (* Michael De Vlieger, Dec 16 2019 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Jeffrey Shallit, Dec 16 2019
STATUS
approved