A078262 Sum of the forward and reverse concatenations of 1 to n.

2, 33, 444, 5555, 66666, 777777, 8888888, 99999999, 1111111110, 23333333231, 2345555545332, 244567776755433, 25466789897765534, 2647689001998775635, 274869910212099785736, 28497092031222200795837, 2950719304132232301805938, 305172940514233242402816039

Offset: 1

Author

Amarnath Murthy, Nov 24 2002

Keywords

• base
• nonn

Examples

			a(3) = 123 + 321 = 444, a(10) = 12345678910 + 10987654321 = 23333333231.
		

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..369

Crossrefs

Cf. A000422, A007908, A078263.

Programs

Maple

a:= n-> parse(cat(1+n-i$i=1..n))+parse(cat($1..n)):
seq(a(n), n=1..18);  # Alois P. Heinz, Jun 25 2025

Mathematica

Table[With[{c1=FromDigits[Flatten[IntegerDigits/@Range[n]]],c2= FromDigits[ Flatten[ IntegerDigits/@Range[n,1,-1]]]},c1+c2],{n,20}] (* Harvey P. Dale, Jul 03 2020 *)

Formula

a(n) = A000422(n) + A007908(n). - Sean A. Irvine, Jun 25 2025

Extensions

More terms from Sascha Kurz, Jan 04 2003