

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
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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: A122845 A135203 A251552 * A102818 A010701 A174971
Adjacent sequences: A179801 A179802 A179803 * A179805 A179806 A179807


KEYWORD

easy,nonn,base


AUTHOR

Dominick Cancilla, Jul 27 2010


STATUS

approved



