OFFSET
0,2
COMMENTS
Triangles only occur as pairs forming 2 X 2 squares. For program code and additional details, see A362297.
LINKS
Paolo Xausa, Table of n, a(n) for n = 0..1000
Index entries for linear recurrences with constant coefficients, signature (10,-15).
FORMULA
a(n) = 10*a(n-1) - 15*a(n-2).
G.f.: (1 - 3*x)/(1 - 10*x + 15*x^2).
E.g.f.: exp(5*x)*(5*cosh(sqrt(10)*x) + sqrt(10)*sinh(sqrt(10)*x))/5. - Stefano Spezia, Apr 20 2023
EXAMPLE
a(1)=7:
___ _ _ ___ ___ _ _ ___ ___ _ _ ___ ___ _
| /| | | | /| |\ | | | |\ | |___| | | |___| | | | |
|/__|_| |_|/__| |__\|_| |_|__\| |___|_| |_|___| |_|_|_|
MATHEMATICA
LinearRecurrence[{10, -15}, {1, 7}, 30] (* Paolo Xausa, Jul 20 2024 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Gerhard Kirchner, Apr 19 2023
STATUS
approved