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!)
A308969 Table, read by rows: row n contains the prime divisors of A001008 (numerator of n-th harmonic number), without repetitions. 4
1, 3, 11, 5, 137, 7, 3, 11, 761, 7129, 11, 61, 97, 863, 13, 509, 29, 43, 919, 1049, 1117, 29, 41233, 17, 8431, 37, 1138979, 19, 39541, 37, 7440427, 5, 11167027, 18858053, 3, 23, 53, 227, 761, 583859, 5, 577, 467183, 109, 312408463 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Row 1 is taken to be {1} instead of being empty, by convention.

LINKS

Table of n, a(n) for n=1..45.

EXAMPLE

   n | A001008(n) written as product of primes

-----+---------------------------------------------

   1 | 1 (empty product)

   2 | 3

   3 | 11

   4 | 5 * 5   (So 5 is the only prime divisor, and row(4) = {5}.)

   5 | 137

   6 | 7 * 7

   7 | 3 * 11 * 11       whence row(7) = {3, 11}.)

   8 | 761

   9 | 7129

  10 | 11 * 11 * 61      whence row(10) = {11, 61}.

  11 | 97 * 863

  12 | 13 * 13 * 509     whence row(16) = {13, 509}.

  13 | 29 * 43 * 919     whence row(13) = {29, 43, 919}.

  14 | 1049 * 1117

  15 | 29 * 41233

  16 | 17 * 17 * 8431    whence row(16) = {17, 8431}.

  17 | 37 * 1138979

  18 | 19 * 19 * 39541   whence row(18) = {19, 39541}.

  19 | 37 * 7440427

  20 | 5 * 11167027

etc.

MATHEMATICA

Table[FactorInteger[Numerator[HarmonicNumber[n]]][[All, 1]], {n, 30}]// Flatten (* Harvey P. Dale, Sep 14 2020 *)

PROG

(PARI) row(n)={if(n>1, factor(A001008(n))[, 1]~, [1])}

CROSSREFS

Cf. A001008.

Cf. A308967 (number of prime factors), A308968 (table of factorization), A308970 & A308971 (smallest & greatest prime factor) of A001008(n).

Sequence in context: A212402 A114234 A242223 * A308970 A308971 A120299

Adjacent sequences:  A308966 A308967 A308968 * A308970 A308971 A308972

KEYWORD

nonn,tabf

AUTHOR

M. F. Hasler, Jul 03 2019

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 April 17 23:03 EDT 2021. Contains 343071 sequences. (Running on oeis4.)