A116980 Number of ways to arrange integers 1...n so that the sum of each adjacent pair is a triangular number, not counting reversals.

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

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