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A256122 Number of iterations needed to reach 0 or 1 under the map n-> n-sopf(n), where sopf(n) is the sum of the distinct primes dividing n (A008472). 1
0, 1, 1, 2, 1, 1, 1, 2, 2, 2, 1, 2, 1, 2, 2, 3, 1, 2, 1, 2, 2, 3, 1, 2, 3, 2, 3, 2, 1, 3, 1, 4, 2, 3, 2, 2, 1, 2, 2, 3, 1, 4, 1, 2, 2, 3, 1, 2, 5, 2, 2, 2, 1, 6, 3, 2, 3, 4, 1, 3, 1, 2, 2, 3, 2, 3, 1, 6, 2, 3, 1, 2, 1, 3, 2, 4, 2, 4, 1, 2, 5, 3, 1, 3, 3, 2, 4 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,4

LINKS

Michel Lagneau, Table of n, a(n) for n = 1..10000

EXAMPLE

a(16) = 3 because:

16 - sopf(16) = 16 - 2 = 14 (first iteration);

14 - sopf(14) = 14 - 9 = 5 (second iteration);

5 - sopf(5)= 5 - 5 = 0 (third iteration and reaching 0).

a(22) = 3 because:

22 - sopf(22) = 22 - 13 = 9 (first iteration);

9 - sopf(9) = 9 - 3 = 6 (second iteration);

6 - sopf(6)= 6 - 5 = 1 (third iteration and reaching 1).

MAPLE

A008472:= n -> add(d, d = select(isprime, numtheory[divisors](n))):

  A:= proc(n)

        a := 0 ;

        x := n ;

        while x>1 do

                x := x-A008472(x) ;

                a := a+1 ;

        end do:

        a ;

end proc:

seq(A(n), n=1..100);

MATHEMATICA

t[n_] := -1 + Length[NestWhileList[#-Total[Transpose[FactorInteger[#]][[1]]]&, n, #>1&]]; Table[t[n], {n, 100}]

CROSSREFS

Cf. A008472.

Sequence in context: A079487 A229122 A069010 * A087048 A109700 A087742

Adjacent sequences:  A256119 A256120 A256121 * A256123 A256124 A256125

KEYWORD

nonn

AUTHOR

Michel Lagneau, Mar 15 2015

STATUS

approved

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Last modified August 7 12:19 EDT 2020. Contains 336276 sequences. (Running on oeis4.)