OFFSET
0,7
EXAMPLE
10!! = 10*8*6*4*2 = 3840 -> 3+8+4+0 = 15 -> 1+5 = 6 -> persistence = 2.
MAPLE
with(numtheory): with(combinat): P:=proc(n) local a, t; t:=0; if n mod 2=0 then a:=2^(n/2)*(n/2)!; else a:=(n+1)!/(2^((n+1)/2)*((n+1)/2)!); fi;
while a>9 do t:=t+1; a:=convert(convert(a, base, 10), `+`); od; t;
end: seq(P(i), i=0..10^2);
CROSSREFS
KEYWORD
easy,nonn,base
AUTHOR
Paolo P. Lava and Giorgio Balzarotti, Jun 19 2007, corrected Jun 22 2007
EXTENSIONS
Corrected entries and Maple code by Paolo P. Lava, Dec 19 2017
STATUS
approved