

A182173


Number of inequivalent expressions involving n operands.


1



2, 10, 94, 1466, 31814, 887650, 30259198, 1218864842, 56644903958, 2983300619410, 175598066553166, 11423394497044154, 813897286250604326, 63030237104398839490, 5271647928235911880222, 473558482553909252128298, 45473767604938843870986422, 4648336478135316689480390770
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OFFSET

1,1


COMMENTS

Each operand must be used exactly once, and the only allowed operations are addition, subtraction, multiplication, division, and unary minus. Parentheses are permitted. This sequence differs from A140606 by allowing unary minus.


LINKS

David Radcliffe, Table of n, a(n) for n = 1..90
David Radcliffe, Python script
Wikipedia, 24 Game


EXAMPLE

When n=2, there are 10 inequivalent expressions: a+b, ab, ba, ab, a*b, a*b, a/b, a/b, b/a, b/a.


CROSSREFS

Cf. A140606.
Sequence in context: A231375 A100622 A103436 * A160940 A193290 A193435
Adjacent sequences: A182170 A182171 A182172 * A182174 A182175 A182176


KEYWORD

nonn


AUTHOR

David Radcliffe, Apr 16 2012


STATUS

approved



