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A175125 a(n) is the number of numbers m such that the number of iterations of r -> r - (largest divisor d < r) needed to reach 1 starting at r = m is equal to n. 5
1, 1, 2, 3, 5, 9, 13, 23, 36, 65, 100, 175, 275, 468, 760, 1266, 2077, 3454, 5690, 9449, 15547, 25709, 42459, 70181, 115947, 191509, 316570, 523087, 864406, 1428174, 2359266 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

Table of n, a(n) for n=0..30.

EXAMPLE

Example (a(4)=5): There are five numbers (7,9,10,12,16) with 4 steps of defined iteration: 7-1=6, 6-3=3, 3-1=2, 2-1=1; 9-3=6, 6-3=3, 3-1=2, 2-1=1; 10-5=5, 5-1=4, 4-2=2, 2-1=1; 12-6=6, 6-3=3, 3-1=2, 2-1=1; 16-8=8, 8-4=4, 4-2=2, 2-1=1.

PROG

(PARI) a064097(n)={my(k=1, d=divisors(n), r=n-d[#d-1]); while(r>1, d=divisors(r); r-=d[#d-1]; k++); k};

my(c=vector(50)); for(k=2, 2^20, j=a064097(k); c[j]++); concat([1], c[1..20]) \\ Hugo Pfoertner, Mar 23 2020

CROSSREFS

Cf. A000079, A064097, A105017.

Sequence in context: A018138 A336631 A228129 * A171925 A186946 A057225

Adjacent sequences: A175122 A175123 A175124 * A175126 A175127 A175128

KEYWORD

nonn,more

AUTHOR

Jaroslav Krizek, Feb 15 2010

EXTENSIONS

a(8)-a(27) from Hugo Pfoertner, Mar 23 2020

a(28)-a(30) from Robert G. Wilson v, Apr 05 2020

STATUS

approved

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Last modified November 27 06:50 EST 2022. Contains 358362 sequences. (Running on oeis4.)