OFFSET
1,1
COMMENTS
The sequence starts with a(1) = 2 and is always extended with the smallest integer not yet present in the sequence and not leading to a contradiction.
LINKS
Jean-Marc Falcoz, Table of n, a(n) for n = 1..300
FORMULA
a(n) = c(n) - c(n-1), where c(n) = concatenation of the first n digits, c(n) ~ 0.22*10^n, a(n) ~ 0.198*10^n. See A300000 for the proof. - M. F. Hasler, Feb 22 2018
EXAMPLE
2 + 20 = 22 which is the concatenation of 2 and 2.
2 + 20 + 198 = 220 which is the concatenation of 2, 2 and 0.
2 + 20 + 198 + 1981 = 2201 which is the concatenation of 2, 2, 0 and 1.
PROG
(PARI) a(n, show=1, a=2, c=a, d=[c])={for(n=2, n, show&&print1(a", "); a=-c+c=c*10+d[1]; d=concat(d[^1], if(n>2, digits(a)))); a} \\ M. F. Hasler, Feb 22 2018
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Eric Angelini and Jean-Marc Falcoz, Feb 21 2018
STATUS
approved