A332415 a(n) is the number of distinct valid solutions taking into account the ambiguity of open and closed absolute value bars for an input of -1 to -2*(n)-1 with absolute value bars between each (|-1|, |-1|-2|-3|, |-1|-2|-3|-4|-5|, etc.).

1, 2, 5, 13, 39, 124, 403, 1304, 4301, 14370, 47575, 157153, 512311, 1663977, 5446573

Offset

1,2

Comments

a(5) is the solution to Jim Propp's submitted problem published in FiveThirtyEight's "The Riddler" column.

Links

Table of n, a(n) for n=1..15.

FiveThirtyEight, Problem origin

Twitter, Initial Observation

Example

For n = 2 (input of |-1|-2|-3|-4|-5|) the solutions are 5 and -5, so a(2) = 2.

Crossrefs

Sequence in context: A151446 A239106 A022894 * A149861 A148305 A104447

Adjacent sequences: A332412 A332413 A332414 * A332416 A332417 A332418

Keyword

nonn,more

Author

Tyler Barron, Feb 12 2020

Status

approved