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 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 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

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Last modified December 1 07:14 EST 2020. Contains 338833 sequences. (Running on oeis4.)