OFFSET
1,5
COMMENTS
A sum pyramid for n is defined to be a pyramid with n at its apex, all pairs of adjacent members (x, y) of rows 2,3,4,... sum to the element immediately above, every element is positive and distinct, rows are complete (length of row m = length of row (m-1) + 1), reflections are not counted, and the pyramid is maximal (i.e., not part of a larger pyramid that qualifies). An example of the meaning of "maximal" can be seen in the Example section: the pyramids
.
9 9
6 3 and 5 4
.
are not counted because they consist of the top 2 rows of larger (3-row) pyramids that are counted. [Clarified by Peter Munn, Nov 20 2021]
LINKS
J. Stauduhar, Python program
EXAMPLE
The five pyramids for a(9) are:
9 9 9
9 9 6 3 6 3 5 4
8 1 7 2 5 1 2 4 2 1 2 3 1
PROG
(Python) See Links section.
CROSSREFS
KEYWORD
nonn
AUTHOR
J. Stauduhar, Jul 21 2021
EXTENSIONS
Definition aligned with A028307 by Peter Munn, Nov 20 2021
STATUS
approved