login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A249671 Integers n such that A249670(n) = n. 1
1, 364, 86800, 90768, 149856, 632400, 828816, 46462800, 61987600, 148468320, 153972000, 185684160, 187465824, 189300384, 191659104, 193808160, 196219296, 202460352, 204118464, 215399520, 220116960, 221931360, 222778080, 223382880, 228584160, 338116680 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

That is, integers n such that A017665(n)*A017666(n) = n.

LINKS

Table of n, a(n) for n=1..26.

EXAMPLE

sigma(364)/364 = 28/13 and 28*13 = 364, so 364 is in the sequence.

MATHEMATICA

lista[n_Integer] := Select[Range[n], # == Numerator[DivisorSigma[-1, #]] * Denominator[DivisorSigma[-1, #]] &];

lista[10^6] (* Michael De Vlieger, Nov 10 2014 *)

PROG

(PARI) isok(n) = my(ab = sigma(n)/n); numerator(ab)*denominator(ab) == n; \\ Michel Marcus, Nov 04 2014

CROSSREFS

Cf. A017665, A017666, A249670.

Sequence in context: A278002 A107509 A140935 * A022196 A098252 A221393

Adjacent sequences:  A249668 A249669 A249670 * A249672 A249673 A249674

KEYWORD

nonn

AUTHOR

Michel Marcus, Nov 03 2014

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 26 11:46 EDT 2019. Contains 322472 sequences. (Running on oeis4.)