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
KEYWORD
nonn,base
AUTHOR
Paul Curtz, Oct 03 2007
STATUS
approved