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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 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 * A102818 A010701 A290858 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 December 16 09:06 EST 2019. Contains 330020 sequences. (Running on oeis4.)