OFFSET
1,1
COMMENTS
FORMULA
a(n) = 5*10^(n-1) + ceiling(10^(n/2)) for n >= 2.
EXAMPLE
floor(7^2/10) = 4, floor(8^2/10) = 6, and 8 is the smallest k such that floor(k^2/10) - floor((k - 1)^2/10) = 2, so a(1) = 8.
floor(59^2/10) = 34, floor(60^2/10) = 36, and 60 is the smallest k such that floor(k^2/100) - floor((k - 1)^2/100) = 2, so a(2) = 60.
PROG
(PARI) a(n) = if(n==1, 8, 5*10^(n-1) + ceil(10^(n/2)))
CROSSREFS
KEYWORD
nonn
AUTHOR
Jianing Song, Dec 22 2018
STATUS
approved