A102484 Numbers of the concatenated form 9nn9.

9009, 9119, 9229, 9339, 9449, 9559, 9669, 9779, 9889, 9999, 910109, 911119, 912129, 913139, 914149, 915159, 916169, 917179, 918189, 919199, 920209, 921219, 922229, 923239, 924249, 925259, 926269, 927279, 928289, 929299, 930309

Offset: 1

Author

Mark Hudson (mrmarkhudson(AT)hotmail.com), Jan 12 2005

Keywords

• easy
• nonn
• base

Examples

			For n=0 we concatenate 3, 0, 0 and 3 to get 3003.
For n=10 we concatenate 3, 10, 10 and 3 to get 310103.
		

Links

• Robert Israel, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A100846 for 1nn1; A100896 for 3nn3; A100897 for 7nn7.

Cf. A055642.

Programs

Maple

f:= n -> 9 + 9*10^(2*ilog10(n-1)+3)+(n-1)*(10+10^(2+ilog10(n-1))):
f(1):= 9009;
map(f, [$1..200]); # Robert Israel, May 09 2017

Mathematica

With[{k = {9}}, Table[FromDigits@ Join[k, #, #, k] &@ IntegerDigits[n], {n, 0, 30}]] (* Michael De Vlieger, May 09 2017 *)

Formula

a(n) = 9*(1 + 10^(2*A055642(n-1)+1))+(n-1)*(10+10^(1+A055642(n-1))). - Robert Israel, May 09 2017