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A145549 Number of distinct values taken by 9^9^...^9 (with n 9's and parentheses inserted in all possible ways). 15
1, 1, 2, 4, 9, 20, 48, 115, 286, 719, 1842, 4766, 12485, 32969, 87795, 235326, 634664, 1720573, 4686829, 12820504, 35204254, 97001655, 268120807, 743236814, 2065709551, 5755253457 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

The subsequence of primes begins 2, 719, 32969. No more through a(26). [Jonathan Vos Post, Apr 02 2011]

LINKS

Table of n, a(n) for n=1..26.

R. K. Guy and J. L. Selfridge, The nesting and roosting habits of the laddered parenthesis, Amer. Math. Monthly 80 (8) (1973), 868-876.

Jonathan Vos Post, The Four Nines problem.

Index entries for sequences related to parenthesizing

CROSSREFS

Cf. A002845, A003018, A003019, A145545, A145546, A145547, A145548, A145550, A000081.

Sequence in context: A292555 A318804 A318857 * A292556 A145550 A000081

Adjacent sequences:  A145546 A145547 A145548 * A145550 A145551 A145552

KEYWORD

more,nonn

AUTHOR

Jon E. Schoenfield, Oct 13 2008

STATUS

approved

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Last modified October 15 16:01 EDT 2018. Contains 316236 sequences. (Running on oeis4.)