%I #26 Jun 10 2026 15:46:20

%S 4,5,6,7,8,14,15

%N Numbers k such that A003266(k) - 1 is prime.

%C The a(n)-th almost-Fibonorial number is prime.

%C If it exists, a(8) > 1300. - _Michael S. Branicky_, Aug 17 2024

%H C. K. Caldwell, <a href="https://t5k.org/glossary/page.php?sort=FibonacciNumber">Fibonacci Numbers</a>.

%H Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Fibonorial.html">Fibonorial</a>.

%t a = 1; Do[ a = a*Fibonacci[n]; If[ PrimeQ[a - 1], Print[n] ], {n, 1, 247} ]

%t Position[FoldList[Times,Fibonacci[Range[20]]],_?(PrimeQ[#-1]&)]//Flatten (* _Harvey P. Dale_, Jun 10 2026 *)

%Y Cf. A003266, A053408.

%K nonn,more

%O 1,1

%A _Robert G. Wilson v_, Feb 07 2001

%E Definition corrected by _Daniel Forgues_, Nov 29 2009

%E Name edited by _Michel Marcus_, Jan 17 2024