A234932 The product a(n)*a(n+1) can be written using the digits of {a(n),a(n+1)}; always choose the smallest possible unused positive integer.

1, 2, 10, 3, 51, 30, 100, 4, 16, 40, 160, 352, 151, 34, 106, 25, 13, 24, 26, 240, 130, 250, 133, 295, 313, 1000, 5, 19, 50, 102, 6, 21, 60, 127, 171, 241, 175, 109, 45, 181, 450, 187, 400, 166, 3052, 1196, 302, 2865, 1441, 298, 31, 1165, 139, 7, 1015, 70, 1043, 700, 1168, 412, 1702, 125

Offset

1,2

Comments

Inspired by A228276.

Links

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

E. Angelini, Add A to B

E. Angelini, Add A to B [Cached copy, with permission]

Example

1*2 = 2 uses only digits from {1,2},
2*10 = 20 uses only digits from {2,1,0},
10*3 = 30 uses only digits from {1,0,3}.
What comes after 3? Call it x. 3*x must use only digits from 3 and the digits of x. Surprisingly x=51 is the first (unused) number which works.
And so on.

Prog

(Haskell)
import Data.List ((\\), delete)
a234932 n = a234932_list !! (n-1)
a234932_list = 1 : f 1 [2..] where
   f x zs = g zs where
     g (y:ys) = if null $ show (x * y) \\ (show x ++ show y)
                   then y : f y (delete y zs) else g ys
-- Reinhard Zumkeller, Jul 26 2014

Crossrefs

Cf. A228276

Sequence in context: A153273 A276486 A341363 * A332701 A342158 A344544

Adjacent sequences: A234929 A234930 A234931 * A234933 A234934 A234935

Keyword

nonn,base,nice

Author

Claudio Meller, Jan 01 2014

Extensions

Entered by N. J. A. Sloane on Claudio Meller's behalf and submitted for the 2014 JMM competition with his permission.

Status

approved