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!)
A218993 Numerator of the least reduced fraction b/c > 1 using divisors b and c of n. 4
2, 3, 2, 5, 3, 7, 2, 3, 2, 11, 4, 13, 2, 5, 2, 17, 3, 19, 5, 7, 2, 23, 4, 5, 2, 3, 7, 29, 6, 31, 2, 3, 2, 7, 4, 37, 2, 3, 5, 41, 7, 43, 2, 5, 2, 47, 4, 7, 2, 3, 2, 53, 3, 11, 8, 3, 2, 59, 6, 61, 2, 9, 2, 13, 3, 67, 2, 3, 7, 71, 9, 73, 2, 5, 2, 11, 3, 79, 5, 3, 2 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,1

COMMENTS

The product b*c divides n.  Does every positive integer except one occur infinitely many times?

LINKS

Clark Kimberling, Table of n, a(n) for n = 2..10000

EXAMPLE

For n = 2,...,12, the fractions are 2/1, 3/1, 2/1, 5/1, 3/2, 7/1, 2/1, 3/1, 2/1, 11/1, 4/3, so that

A218993 = (2, 3, 2, 5, 3, 7, 2, 3, 2, 11, 4, ... );

A219093 = (1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 3, ... );

A219094 = (1, 1, 2, 1, 1, 1, 4, 3, 5, 1, 1, ... );

A219095 = (6, 12, 15, 18, 20, 21, 24, 28, 30, 35, 36, ... ).

MATHEMATICA

f[n_] := Divisors[n];

t = Table[Min[Table[f[n][[i + 1]]/f[n][[i]], {i, 1, -1 + Length[f[n]]}]], {n, 2, 200}];

tn = Numerator[t]  (* A218993 *)

td = Denominator[t] (* A219093 *)

Table[n/(tn[[n - 1]]*td[[n - 1]]),

   {n, 2, 100}]  (* A219094 *)

p[n_] := If[IntegerQ[t[[n]]], 0, 1]

u = Table[p[n], {n, 1, Length[t]}]; 1 + Flatten[Position[u, 1]]  (* A219095 *)

CROSSREFS

Cf. A219093, A219094, A219095.

Sequence in context: A210437 A109674 A284260 * A067629 A079870 A185642

Adjacent sequences:  A218990 A218991 A218992 * A218994 A218995 A218996

KEYWORD

nonn,easy

AUTHOR

Clark Kimberling, Feb 06 2013

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 July 24 05:05 EDT 2021. Contains 346273 sequences. (Running on oeis4.)