OFFSET
1,3
COMMENTS
Records occur at indices 1, 2, 3, 5, 7, 9, 13, 17, 21, 33, 37, 45, 57, 105, 145, 217, 225, 273, 385, 495, 561, 651, 705, 945, 1105, ... - Peter Kagey, Nov 18 2020
LINKS
Peter Kagey, Table of n, a(n) for n = 1..5000
OEIS Wiki, Figurate numbers: Polygonal numbers
EXAMPLE
The a(9) = 6 ways of writing 9 as the difference of two k-gonal numbers are:
MATHEMATICA
b := 74
CoefficientList[
Series[Sum[
Sum[x^(k*(p*k - (p - 2))/2)*x^(p*k)/(1 - x^(p*k)), {k, 1, b}], {p,
1, b - 1}], {x, 0, b}], x]
CROSSREFS
KEYWORD
nonn
AUTHOR
Peter Kagey, Apr 07 2020
STATUS
approved