OFFSET
1,1
COMMENTS
All terms are hypotenuse numbers (A009003).
Each term is the hypotenuse of a Pythagorean triangle T whose legs, say u and v, are also the hypotenuses of Pythagorean triangles, say U and V, and U and V have a leg of the same length. This can be summarized as follows:
a(n)^2
/ \
/ \
/ T \
u^2-----v^2
/ \ / \
/ \ / \
/ U \ / V \
i^2-----j^2-----k^2
Any positive multiple of a term is also a term (see A338892 for the primitive terms).
LINKS
Rémy Sigrist, Table of n, a(n) for n = 1..10000
Rémy Sigrist, C# program for A338890
EXAMPLE
Regarding 169:
- we have 169^2 = 65^2 + 156^2, 65^2 = 25^2 + 60^2, 156^2 = 60^2 + 144^2:
169^2
/ \
/ \
/ \
65^2--156^2
/ \ / \
/ \ / \
/ \ / \
25^2---60^2----144^2
- so 169 belongs to the sequence.
PROG
(C#) See Links section.
CROSSREFS
KEYWORD
nonn
AUTHOR
Rémy Sigrist, Nov 14 2020
STATUS
approved