

A003019


Number of distinct values taken by 4^4^...^4 (with n 4's and parentheses inserted in all possible ways).
(Formerly M1179)


17



1, 1, 2, 4, 9, 20, 48, 114, 282, 703, 1787, 4583, 11900, 31131, 82117, 217954, 581970, 1561704, 4210263, 11396488, 30963024, 84402984, 230779071, 632762424, 1739387089
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OFFSET

1,3


COMMENTS

See also the Four Fours puzzle [Bourke]. Four fours is a mathematical puzzle. The goal of four fours is to find the simplest mathematical expression for every whole number from 0 to some maximum, using only common mathematical symbols and the digit four (no other digit is allowed). The subsequence of primes begins 2, 1787, 4583, no more through a(23). [Jonathan Vos Post, Apr 02 2011]


REFERENCES

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).


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KEYWORD

nonn,nice,more


AUTHOR



EXTENSIONS



STATUS

approved



