A109214 Product of a(n-1) and digit reversal of a(n-2).

1, 2, 2, 4, 8, 32, 256, 5888, 3838976, 34109301760, 231888097227054080, 1556059601911449331359933440, 125186119679477750610733678211850458005934080, 55507466796083630515105997822341552764197877620395801846452095434158080

Offset: 1

Author

Zak Seidov, Jun 22 2005

Keywords

• base
• nonn
• changed

Comments

The next term (a(15)) has 115 digits. - Harvey P. Dale, Nov 14 2011

Crossrefs

Cf. A000301 (a(n) = a(n-1)*a(n-2)), A004086 (R(n) = digit reversal of n), A109213 (a(n) = a(n-2)*R(a(n-1))).

Programs

Maple

R:= n-> (s-> parse(cat(s[-i]$i=1..length(s))))(""||n):
a:= proc(n) option remember; `if`(n<3, n, a(n-1)*R(a(n-2))) end:
seq(a(n), n=1..14);  # Alois P. Heinz, Sep 01 2025

Mathematica

a[1]=1;a[2]=2;a[n_]:=a[n]=a[n-1]*FromDigits[Reverse[IntegerDigits[a[n-2]]]]; A109214=Table[a[n], {n, 13}]
Transpose[NestList[{Last[#],Last[#]FromDigits[Reverse[ IntegerDigits[ First[ #]]]]}&,{1,2},13]][[1]] (* Harvey P. Dale, Nov 14 2011 *)

Formula

a(n) = a(n-1)*R(a(n-2)).

Extensions

One more term (a(14)) from Harvey P. Dale, Nov 14 2011