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A179804 Number of letter combinations on a standard telephone keypad represented by the digits in n 0
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: A073139 A122845 A135203 * A102818 A010701 A174971

Adjacent sequences:  A179801 A179802 A179803 * A179805 A179806 A179807

KEYWORD

easy,nonn,base

AUTHOR

Dominick Cancilla, Jul 27 2010

STATUS

approved

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Last modified April 17 11:46 EDT 2014. Contains 240635 sequences.