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A341208
a(n) = F(n+4) * F(n+1) - 4 * (-1)^n where F(n) = A000045(n) are the Fibonacci numbers.
3
9, 12, 43, 101, 276, 711, 1873, 4892, 12819, 33549, 87844, 229967, 602073, 1576236, 4126651, 10803701, 28284468, 74049687, 193864609, 507544124, 1328767779, 3478759197, 9107509828, 23843770271, 62423801001, 163427632716, 427859097163, 1120149658757
OFFSET
1,1
COMMENTS
First differences of A338225.
Also it is second differences between the areas of consecutive rectangles with side lengths F(n+3) and F(n).
REFERENCES
Burak Muslu, Sayılar ve Bağlantılar, Luna, 2021, p. 51.
FORMULA
a(n) = F(n+4) * F(n+1) - 4 * (-1)^n for n > 0.
G.f.: x*(9 - 6*x + x^2)/(1 - 2*x - 2*x^2 + x^3).
EXAMPLE
For n = 2, a(2) = F(2+4) * F(2+1) - 4 * (-1)^2 = 8 * 2 - 4 = 12.
PROG
(PARI) a(n) = fibonacci(n+4)*fibonacci(n+1) - 4*(-1)^n; \\ Michel Marcus, Feb 06 2021
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Burak Muslu, Feb 06 2021
STATUS
approved