login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A110545 a(n) is smallest positive integer m such that n divides either the numerator or the denominator of the (reduced) fraction H(m) = Sum_{k=1..m} 1/k. 3
1, 2, 2, 4, 4, 3, 6, 8, 9, 5, 3, 4, 12, 7, 5, 16, 16, 9, 18, 5, 9, 11, 22, 9, 4, 13, 27, 7, 13, 5, 30, 32, 7, 17, 7, 9, 17, 19, 13, 8, 40, 9, 13, 11, 9, 23, 46, 16, 6, 25, 17, 13, 22, 27, 11, 8, 19, 29, 58, 5, 10, 31, 9, 64, 13, 11, 66, 17, 22, 7, 70, 9, 72, 37, 25, 19, 11, 13, 78, 16, 81 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

For values of n such that a(n) = n, see A113570; this begins: 1, 2, 4, 8, 9, 16, 27, 32, 64, 81, ...

Conjecture: a(n) <= n for all positive n's.

LINKS

Michel Marcus, Table of n, a(n) for n = 1..1000

EXAMPLE

a(5) = 4 because H(4) = 25/12 is the first harmonic number with either its numerator or denominator divisible by 5.

a(6) = 3 because H(3) = 11/6 is the first harmonic number with either its numerator or denominator divisible by 6.

MATHEMATICA

f[n_] := Block[{h = k = 1}, While[ !IntegerQ[ Numerator[h]/n] && !IntegerQ[ Denominator[h]/n], k++; h = h + 1/k]; k]; Table[ f[n], {n, 81}] (* Robert G. Wilson v, Sep 28 2005 *)

PROG

(PARI) isok(h, n) = ((numerator(h) % n) == 0) || ((denominator(h) % n) == 0);

h(n) = sum(k=1, n, 1/k);

a(n) = {my(k = 1); while(! isok(h(k), n), k++); k; } \\ Michel Marcus, Jul 23 2017

CROSSREFS

Cf. A001008, A002805, A113570.

Sequence in context: A205450 A215674 A279211 * A104798 A243238 A169629

Adjacent sequences:  A110542 A110543 A110544 * A110546 A110547 A110548

KEYWORD

nonn

AUTHOR

Leroy Quet, Sep 11 2005

EXTENSIONS

More terms from Robert G. Wilson v, Sep 28 2005

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 May 12 13:46 EDT 2021. Contains 343823 sequences. (Running on oeis4.)