This constant is mentioned in GKP book : Concrete Mathematics, by Ron Graham, Donald E Knuth, Oren Patashnik page 478 and 571. Addison Wesley, 1990. 1.2267420107203532444176302304553616558714096904402504196432973012140221383153\ 121684526215624947977412591332334004120027440664103145209506733881793040788634\ 483048008841808185478343494023885863335310549643887562213037246127723118581180\ 56699615948964051109218 is 256 digits of that constant C. The Fibonacci factorials, FF(n) are the Product(Fibonacci(k),k=1..n) so FF(5) = 1*1*2*3*5 = 30 and FF(100) = roughly 10 ** 1021. Since F(n) is {phi**n/sqrt(5)} , rounded to the nearest integer , then we can easily say that FF(n) will be roughly phi**(n*(n+1)/2)/sqrt(5)**n (1) where phi is the Golden ratio = 1/2 + sqrt(5)/2, so by examining the sum of the log of F(n) (the fibonacci sequence) we can expand it to find more precisely that the expression (1) will involve a constant C, namely FF(n) = C * phi**(n*(n+1)/2)/sqrt(5)**n and that C = (1-a)*(1-a**2)*(1-a**3)... 1.2267420... where a = -1/phi**2. This product (with a) is the inverse of the partition function where the exponents are pentoganal numbers, maybe there is a closed expression for C ?? For further details see GKP book page 571. # This is the electronic signature for Plouffe's Inverter # # Ceci est la signature électronique pour l'Inverseur de Plouffe # # Copyright : Simon Plouffe/Plouffe's Inverter (c) 1986. # # http://www.lacim.uqam.ca/pi #