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!)
A264907 a(n) is the smallest "cyclic" integer, k, that has exactly n prime factors. 0
2, 15, 255, 5865, 170085, 9014505, 1661569239, 117971415969, 494390700895, 42163217429333, 2571956263189313, 551363902358334637 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The cyclic numbers are given in A003277.

a(n) = k if k = p_1*p_2*...*p_n  where the p_i are distinct primes and no p_j-1 is divisible by any p_i and k is the smallest such integer.

LINKS

Table of n, a(n) for n=1..12.

EXAMPLE

The prime factorizations for the first 12 terms are:

   2

   3,  5

   3,  5, 17

   3,  5, 17, 23

   3,  5, 17, 23, 29

   3,  5, 17, 23, 29, 53

   3, 11, 17, 29, 41, 47, 53

   3, 11, 17, 29, 41, 47, 53, 71

   5,  7, 13, 17, 19, 23, 37, 59, 67

   7, 11, 13, 17, 19, 31, 37, 41, 47, 59

   7, 11, 13, 17, 19, 31, 37, 41, 47, 59, 61

  11, 13, 17, 19, 29, 31, 37, 41, 43, 47, 61, 71

MATHEMATICA

(* about 45 seconds on laptop computer *)

f[list_] := Boole[Map[Apply[Divisible, #] &,

   Level[Table[Table[{list[[i]] - 1, list[[j]]}, {i, j + 1, Length[list]}], {j, 1, Length[list] - 1}], {2}]]]; Prepend[Map[Apply[Times, #] &,

  Table[First[Select[Subsets[Table[Prime[n], {n, 2, 18}], {k}],

     Total[f[#]] == 0 &]], {k, 2, 10}]], 2]

CROSSREFS

Cf. A003277.

Sequence in context: A221100 A203310 A102555 * A195737 A192567 A143886

Adjacent sequences:  A264904 A264905 A264906 * A264908 A264909 A264910

KEYWORD

nonn,more

AUTHOR

Geoffrey Critzer, Nov 28 2015

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 March 29 20:20 EDT 2020. Contains 333117 sequences. (Running on oeis4.)