

A116980


Number of ways to arrange integers 1...n so that the sum of each adjacent pair is a triangular number, not counting reversals.


0



1, 1, 1, 0, 0, 0, 0, 0, 0, 1, 1, 4, 19, 23, 16, 43, 59, 66, 127, 492, 886, 964, 2595, 11426, 36780, 78070, 131232, 423402, 1302893, 3356226, 6673924, 16604441, 32195439, 69328860
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OFFSET

0,12


LINKS

Table of n, a(n) for n=0..33.


EXAMPLE

a(9)=1, since {3,7,8,2,4,6,9,1,5} and its reversal are the only permutations
of 1..9 with the given property. Here 3+7, 7+8, 8+2, 4+6, 6+9, 9+1 and 1+5 are all triangular numbers.


CROSSREFS

Cf. A051239.
Sequence in context: A043056 A012879 A072178 * A296602 A022135 A192193
Adjacent sequences: A116977 A116978 A116979 * A116981 A116982 A116983


KEYWORD

nonn


AUTHOR

Giovanni Resta, Apr 01 2006


EXTENSIONS

a(29)a(33) from Donovan Johnson, Aug 27 2010
a(0)=1 prepended by Alois P. Heinz, Oct 05 2020


STATUS

approved



