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A136308 a(n) = (10^2^n - 1)/9. 4
1, 11, 1111, 11111111, 1111111111111111, 11111111111111111111111111111111, 1111111111111111111111111111111111111111111111111111111111111111 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

More generally, reading in base B >= 2: a(n) = (B^2^n - 1)/(B-1).

Recurrence: a(n) = a(n-1)*(B^K + 1) and a(0)=1 where K = floor(log_B a(n-1)) + 1.

B = 2 gives A051179; B = 3 gives A059918.

LINKS

Table of n, a(n) for n=0..6.

FORMULA

a(n) = a(n-1)*(10^K + 1) and a(0)=1 where K=floor(log_10 a(n-1)) + 1 = 2^n + 1.

a(n) = A000042(A000079(n)) = A007088(A051179(n)) = A007089(A059918(n)).

MATHEMATICA

(10^2^Range[0, 10] - 1)/9 (* G. C. Greubel, Apr 19 2021 *)

PROG

(MAGMA) A136308 := func<n|(10^2^n-1)/9>; [A136308(n):n in[0..7]];

(Sage) [(10^2^n -1)/9 for n in (0..10)] # G. C. Greubel, Apr 19 2021

CROSSREFS

Cf. A000042 (repunits).

In other bases: A051179, A059918.

Sequence in context: A340549 A260077 A068053 * A343837 A303067 A075600

Adjacent sequences:  A136305 A136306 A136307 * A136309 A136310 A136311

KEYWORD

easy,nonn

AUTHOR

Ctibor O. Zizka, Mar 22 2008

EXTENSIONS

Edited by Jason Kimberley, Dec 18 2012

STATUS

approved

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Last modified June 13 00:57 EDT 2021. Contains 344980 sequences. (Running on oeis4.)