OFFSET
1,3
COMMENTS
A subsequence of A010784. - FUNG Cheok Yin, Jul 05 2018
LINKS
FUNG Cheok Yin, Table of n, a(n) for n = 1..1082
EXAMPLE
The keypad is:
+---+---+---+
| 1 | 2 | 3 |
+---+---+---+
| 4 | 5 | 6 |
+---+---+---+
| 7 | 8 | 9 |
+---+---+---+
| 0 | x |
+---+---+---+
It is visibly obvious that 5807 can be formed on the keypad.
MATHEMATICA
g = Graph[{1 <-> 2, 1 <-> 4,
2 <-> 1, 2 <-> 3, 2 <-> 5,
3 <-> 2, 3 <-> 6,
4 <-> 1, 4 <-> 5, 4 <-> 7,
5 <-> 2, 5 <-> 4, 5 <-> 6, 5 <-> 8,
6 <-> 3, 6 <-> 5, 6 <-> 9,
7 <-> 0, 7 <-> 4, 7 <-> 8,
8 <-> 0, 8 <-> 5, 8 <-> 7, 8 <-> 9,
9 <-> 6, 9 <-> 8}];
f[{a_, b_}] := FindPath[g, a, b, Infinity, All]
ff = f /@ Flatten[Outer[List, r = Range[9], Range[0, 9]], 1];
A280595 = Sort[Join[r, FromDigits /@ Flatten[ff, 1]]] (* Jean-François Alcover, Jan 07 2017 *)
CROSSREFS
KEYWORD
nonn,base,fini,full
AUTHOR
FUNG Cheok Yin, Jan 06 2017
EXTENSIONS
Initial 0 added by N. J. A. Sloane, Feb 05 2017
STATUS
approved