A179804 - OEIS

A179804

Number of letter combinations on a standard telephone keypad represented by the digits in n

0, 3, 3, 3, 3, 3, 3, 3, 3, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 9, 9, 9, 9, 9, 9, 9, 9, 0, 0, 9, 9, 9, 9, 9, 9, 9, 9, 0, 0, 9, 9, 9, 9, 9, 9, 9, 9, 0, 0, 9, 9, 9, 9, 9, 9, 9, 9, 0, 0, 9, 9, 9, 9, 9, 9, 9, 9, 0, 0, 9, 9, 9, 9, 9, 9, 9, 9, 0, 0, 9, 9, 9, 9, 9, 9, 9, 9, 0, 0, 9, 9, 9, 9, 9, 9, 9, 9, 0

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,2

LINKS

Table of n, a(n) for n=1..100.

FORMULA

If n contains a 1 or 0, then a(n) = 0

Otherwise, if d=number of digits in n, then a(n)=3^d.

EXAMPLE

If any digit in n is 1 or 0, then a(n) = 0 because telephone keys 1 and 0 represent no letters

a(2)=3 because "3" on a keypad can represent "d", "e", or "f".

a(23)=9 because "2" on a keypad represents the letters "abc" and "3" represents "def", and there are 9 possible combinations taking one letter from each of these sets in this order.

CROSSREFS

Sequence in context: A135203 A251552 A324497 * A368311 A102818 A010701

Adjacent sequences: A179801 A179802 A179803 * A179805 A179806 A179807

KEYWORD

easy,nonn,base

AUTHOR

Dominick Cancilla, Jul 27 2010

STATUS

approved