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A131664
A string of n 1's repeated n times.
1
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
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
Sequence in context: A290671 A290416 A171230 * A289404 A278787 A279827
KEYWORD
nonn,base
AUTHOR
Paul Curtz, Oct 03 2007
STATUS
approved