login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A130634 Additive persistence of double factorials. 0
0, 0, 0, 0, 0, 1, 2, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 2, 3, 2, 3, 3, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 2, 2, 3, 2, 2 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,7

LINKS

Table of n, a(n) for n=0..87.

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

Cf. A001147.

Sequence in context: A043568 A043543 A237684 * A274828 A257474 A257317

Adjacent sequences:  A130631 A130632 A130633 * A130635 A130636 A130637

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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified November 19 22:34 EST 2019. Contains 329323 sequences. (Running on oeis4.)