A317774 a(n) = A322667(n) + 1.

8, 60, 532, 5100, 50317, 501000, 5003163, 50010000, 500031623, 5000100000, 50000316228, 500001000000, 5000003162278, 50000010000000, 500000031622777, 5000000100000000, 50000000316227767, 500000001000000000, 5000000003162277661, 50000000010000000000

Offset

1,1

Comments

a(n) is the smallest positive integer k such that floor(k^2/10^n) - floor((k - 1)^2/10^n) = 2. The main entries are A322666 and A322667. However, some people may search for this entry.

Links

Table of n, a(n) for n=1..20.

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

Cf. A017936, A322666, A322667.

Sequence in context: A160228 A274746 A366216 * A099337 A356595 A356598

Adjacent sequences: A317771 A317772 A317773 * A317775 A317776 A317777

Keyword

nonn

Author

Jianing Song, Dec 22 2018

Status

approved