OFFSET
0,3
COMMENTS
Prime for n=2,3,4 (a Fermat prime each time); prime for n=6. When is the next prime in the sequence? Semiprime for a(5) = 87 = 3 * 29, a(10) = 127 * 36944480341540763039. a(11) has 36 digits and is the product of 6 primes. a(12) has 57 digits and is the product of 4 primes. a(13) has 92 digits and is the product of at least 4 primes: 123419 * 35173043 * 80-digit-composite, with the second-smallest prime divisor starting with the concatenation of a(2),a(3),a(4). - Jonathan Vos Post, Feb 28 2005
LINKS
Harvey P. Dale, Table of n, a(n) for n = 0..17
EXAMPLE
a(4)=17, a(5)=87, a(6) = 17*87 + 2 = 1481.
MAPLE
a[0]:=1: a[1]:=1: for n from 2 to 13 do a[n]:=a[n-1]*a[n-2]+2 od: seq(a[n], n=0..13); # Emeric Deutsch, Mar 08 2005
MATHEMATICA
nxt[{a_, b_}]:={b, a*b+2}; NestList[nxt, {1, 1}, 15][[;; , 1]] (* Harvey P. Dale, Sep 17 2024 *)
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Miklos Kristof, Feb 28 2005
EXTENSIONS
More terms from Emeric Deutsch, Mar 08 2005
STATUS
approved