A042938 Reverse or triple: if reverse(a(n)) > a(n), a(n+1) = reverse(a(n)), else a(n+1) = 3*a(n).

1, 3, 9, 27, 72, 216, 612, 1836, 6381, 19143, 34191, 102573, 375201, 1125603, 3065211, 9195633, 27586899, 99868572, 299605716, 617506992, 1852520976, 6790252581, 20370757743, 34775707302, 104327121906, 609121723401, 1827365170203, 3020715637281, 9062146911843

Offset

1,2

Links

Robert Israel, Table of n, a(n) for n = 1..1951

Example

Starting with 1, the reverse is 1 and not greater than 1 so the next term is 3. The reverse of 3 is also not greater than 3 and so the next term is 9. The reverse of 9 is not greater than 9 and so the next term is 27. However, the reverse of 27 is 72 which is greater and so the next term in the sequence is 72 and so on.

Maple

reverse:= proc(n)
local L, i, m;
L:= convert(n, base, 10);
  m:= nops(L);
add(L[i]*10^(m-i), i=1..m);
end proc:
a[1]:= 1:
for n from 2 to 100 do
r:= reverse(a[n-1]);
if r > a[n-1] then a[n]:= r
else a[n]:= 3*a[n-1]
fi
od:
seq(a[i], i=1..100); # Robert Israel, Jun 24 2015

Mathematica

rd[n_]:=Module[{rev=FromDigits[Reverse[IntegerDigits[n]]]}, If[rev>n, rev, 3 n]]; NestList[rd, 1, 30] (* Vincenzo Librandi, Jun 24 2015 *)
NestList[If[IntegerReverse[#]>#, IntegerReverse[#], 3#]&, 1, 30] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Jul 09 2018 *)

Prog

(PARI) lista(nn) = {print1(a=1, ", "); for (n=2, nn, r = eval(concat(Vecrev(Str(a)))); if (r > a, a = r, a *= 3); print1(a, ", "); ); } \\ Michel Marcus, Jan 31 2016

Crossrefs

Sequence in context: A103828 A110740 A348555 * A206604 A084707 A193703

Adjacent sequences: A042935 A042936 A042937 * A042939 A042940 A042941

Keyword

base,nonn

Author

Dann Toliver

Extensions

Corrected by Robert Israel, Jun 24 2015

Status

approved