A078263 Product of the forward and reverse concatenations of 1 to n.
1, 252, 39483, 5332114, 670592745, 80779853376, 9449772114007, 1082152022374638, 121932631112635269, 135650052221140070110, 1371589685334334871208531, 14951973660666886818972704952, 161989023197512459256340110001373, 1744593949735321085709329564827297794
Offset: 1
Examples
a(3) = 123*321 = 39483.
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..14); # Alois P. Heinz, Jun 25 2025
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Mathematica
frc[n_]:=Module[{r1=FromDigits[Flatten[IntegerDigits/@Range[n]]], r2 = FromDigits[ Flatten[ IntegerDigits/@Range[n,1,-1]]]},r1*r2]; Array[ frc, 20] (* Harvey P. Dale, Aug 24 2015 *)
Formula
Extensions
More terms from Sascha Kurz, Jan 04 2003
More terms from Sean A. Irvine, Jun 25 2025