The On-Line Encyclopedia of Integer Sequences (OEIS)

A087192 revision #27

A087192

a(n) = ceiling(a(n-1)*4/3), with a(1) = 1.

1, 2, 3, 4, 6, 8, 11, 15, 20, 27, 36, 48, 64, 86, 115, 154, 206, 275, 367, 490, 654, 872, 1163, 1551, 2068, 2758, 3678, 4904, 6539, 8719, 11626, 15502, 20670, 27560, 36747, 48996, 65328, 87104, 116139, 154852, 206470, 275294, 367059, 489412, 652550

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OFFSET

1,2

COMMENTS

If you repeatedly base 64 encode a string, starting with a single character, the length of the string at step n is 4*a(n). - Christian Perfect, Jan 06 2016

LINKS

Robert Israel, Table of n, a(n) for n = 1..7994

FORMULA

Partial sums of A072493. Also indices of records in A087165: A087165(a(n))=n.

MAPLE

A[1]:= 1:

for n from 2 to 100 do A[n]:= ceil(4/3*A[n-1]) od:

seq(A[i], i=1..100); # Robert Israel, Aug 17 2017

MATHEMATICA

a[1] = 1; a[n_] := a[n] = Ceiling[4 a[n - 1]/3]; Table[a@ n, {n, 45}] (* Michael De Vlieger, Jan 06 2016 *)

PROG

(PARI) a(n) = if (n==1, 1, ceil(a(n-1)*4/3)) \\ Michel Marcus, Aug 01 2013