A284385 Number of fixed convex n-iamonds (or polyiamonds with n cells).

2, 3, 6, 8, 6, 7, 12, 15, 8, 9, 18, 18, 8, 15, 24, 23, 12, 12, 24, 30, 12, 17, 36, 31, 14, 21, 30, 30, 18, 24, 42, 42, 14, 21, 48, 38, 14, 33, 48, 45, 24, 18, 42, 54, 24, 35, 66, 48, 20, 36, 48, 44, 24, 40, 72, 63, 18, 27, 72, 60, 26, 51, 66, 62, 36, 30, 60

Offset: 1

Author

Rémy Sigrist, Mar 26 2017

Keywords

• nonn

Comments

Also, the number of ways to write n as p^2-q^2-r^2-s^2 with 0 <= min(q, r, s) and max(q, r, s) < n and max(q+r, r+s, s+q) <= n.

Examples

			See Links section.
		

Links

• Rémy Sigrist, Table of n, a(n) for n = 1..1000
• Rémy Sigrist, Illustration of the first terms
• Rémy Sigrist, C program for A284385
• Eric Weisstein's World of Mathematics, Polyiamond
• Wikipedia, Polyiamond
• Indranil Ghosh, Python Program to compute the first 1000 terms (translated from the C program by _Rémy Sigrist_)

Crossrefs

Cf. A000577, A001420, A096004.