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
Examples
a(3) = 123 + 321 = 444, a(10) = 12345678910 + 10987654321 = 23333333231.
Links
- Harvey P. Dale, Table of n, a(n) for n = 1..369
Programs
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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
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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
Extensions
More terms from Sascha Kurz, Jan 04 2003