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A322034 Let p1 <= p2 <= ... <= pk be the prime factors of n, with repetition; let s = 1/p1 + 1/(p1*p2) + 1/(p1*p2*p3) + ... + 1/(p1*p2*...*pk); a(n) = numerator of s. a(1)=0 by convention. 4
0, 1, 1, 3, 1, 2, 1, 7, 4, 3, 1, 5, 1, 4, 2, 15, 1, 13, 1, 4, 8, 6, 1, 11, 6, 7, 13, 11, 1, 7, 1, 31, 4, 9, 8, 31, 1, 10, 14, 9, 1, 29, 1, 17, 7, 12, 1, 23, 8, 31, 6, 10, 1, 20, 12, 25, 20, 15, 1, 17, 1, 16, 29, 63, 14, 15, 1, 13, 8, 43, 1, 67 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,4

COMMENTS

Note that s < 1 for all n (compare A322036). This follows easily by induction, since when when we increase n by multiplying it by a new (not-smaller) prime, we increase s by less than 1-s.

LINKS

Table of n, a(n) for n=1..72.

EXAMPLE

If n=12 we get the prime factors 2,2,3, and s = 1/2 + 1/4 + 1/12 = 5/6. So a(12) = 5.

The fractions s for n >= 2 are 1/2, 1/3, 3/4, 1/5, 2/3, 1/7, 7/8, 4/9, 3/5, 1/11, 5/6, 1/13, 4/7, 2/5, 15/16, 1/17, 13/18, 1/19, 4/5, 8/21, ...

MAPLE

# This generates the terms starting at n=2:

P:=proc(n) local FM: FM:=ifactors(n)[2]: seq(seq(FM[j][1], k=1..FM[j][2]), j=1..nops(FM)) end: # A027746

f0:=[]; f1:=[]; f2:=[];

for n from 2 to 120 do

a:=0; b:=1; t1:=[P(n)];

for i from 1 to nops(t1) do b:=b/t1[i]; a:=a+b; od;

f0:=[op(f0), a]; f1:=[op(f1), numer(a)]; f2:=[op(f2), denom(a)]; od:

f0;    # s

f1;    # A322034

f2;    # A322035

f2-f1; # A322036

CROSSREFS

Cf. A006022, A027746, A322035, A322036.

A017665/A017666 = sum of reciprocals of all divisors of n.

Sequence in context: A229341 A106790 A078897 * A226629 A249580 A011086

Adjacent sequences:  A322031 A322032 A322033 * A322035 A322036 A322037

KEYWORD

nonn,frac

AUTHOR

N. J. A. Sloane and David James Sycamore, Nov 28 2018

STATUS

approved

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Last modified February 15 20:32 EST 2019. Contains 320138 sequences. (Running on oeis4.)