A281942 Nonnegative numbers whose digits can be formed by typing adjacent keys on a 123-456-789-0XX keypad without repeating a digit.
0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 12, 14, 21, 23, 25, 32, 36, 41, 45, 47, 52, 54, 56, 58, 63, 65, 69, 70, 74, 78, 85, 87, 89, 96, 98, 123, 125, 145, 147, 214, 236, 254, 256, 258, 321, 325, 365, 369, 412, 452, 456, 458, 470, 478, 521, 523, 541, 547, 563, 569, 587, 589, 632, 652, 654, 658, 698, 741
Offset: 1
Examples
The keypad is: +---+---+---+ | 1 | 2 | 3 | +---+---+---+ | 4 | 5 | 6 | +---+---+---+ | 7 | 8 | 9 | +---+---+---+ | 0 | x | x | +---+---+---+ It is visibly obvious that 470 can be formed on the keypad.
Links
- FUNG Cheok Yin, Table of n, a(n) for n = 1..725
Extensions
Initial 0 added by N. J. A. Sloane, Feb 05 2017
Comments