HP 49G Programming Challenge: OEIS A014261, Integers with exclusively Odd Digits

[David Hayden]

Here's a recursive version. The recursive program is stored in the local ←P variable. It finds the 50th number in 0.23s and the 1E6'th in 0.77s on a 50g.

Code:

«
  «
  1 -
  IF DUP 4 >
  THEN
    5 IDIV2 SWAP ←P EVAL @ Get the value for N/5
  ELSE
    0
  END
  10 * @ 10 * F(N/5)
  SWAP 2 * 1 +  @ F(N % 5)
  +
  » → ←P « ←P EVAL »
»