A131664 A string of n 1's repeated n times.

1, 11, 11, 111, 111, 111, 1111, 1111, 1111, 1111, 11111, 11111, 11111, 11111, 11111, 111111, 111111, 111111, 111111, 111111, 111111, 1111111, 1111111, 1111111, 1111111, 1111111, 1111111, 1111111, 11111111, 11111111, 11111111, 11111111

Offset

1,2

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Formula

G.f.: z/(1-z) * Sum_{n>=0} 10^n*z^(n*(n+1)/2).

Maple

seq(((10^n-1)/9)$n, n=1..10); # Robert Israel, Jul 08 2019

Prog

(Python)
from math import isqrt
def A131664(n): return (10**(isqrt(n<<3)+1>>1)-1)//9 # Chai Wah Wu, Oct 17 2022

Crossrefs

Cf. A000042, A002024.

Sequence in context: A290671 A290416 A171230 * A289404 A278787 A279827

Adjacent sequences: A131661 A131662 A131663 * A131665 A131666 A131667

Keyword

nonn,base

Author

Paul Curtz, Oct 03 2007

Status

approved