OFFSET
1,1
LINKS
Paolo P. Lava & Giorgio Balzarotti, Table of n, a(n) for n = 1..11
EXAMPLE
n=7 -> 7!!+1 = 105+1=106 -> R(106)=601 is prime
MAPLE
P:=proc(i) local a, b, k, n, v; v:=array(1..10000); for n from 1 by 1 to i do a:=1; k:=doublefactorial(n)+1; while k>0 do v[a]:=k-(trunc(k/10)*10); k:=trunc(k/10); a:=a+1; od; k:=0; for b from a-1 by -1 to 1 do k:=k+v[b]*10^(a-1-b); od; if isprime(k) then print(k); fi; od; end: P(2000);
CROSSREFS
KEYWORD
nonn
AUTHOR
Paolo P. Lava and Giorgio Balzarotti, Mar 02 2010
STATUS
approved