This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A238330 Numbers n such that rad(sigma(n)) = 2*rad(n), where the "radical" of n, rad(n), is A007947 and sigma(n) is the sum of the divisors of n. 1
 135, 891, 200655, 307125, 544635, 1672125, 2876211, 3138345, 4538625, 5016375, 5417685, 6517665, 11764935, 13179375, 13615875, 14705145, 15049125, 18309375, 40847625, 45623655, 84418425, 98041125, 99684375, 135442125, 153778905, 203870601, 262840851, 270571875 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS First 5 terms from MathOverflow. LINKS Donovan Johnson, Table of n, a(n) for n = 1..91 (terms < 10^11) Sylvain Julien, MathOverflow: rad(sigma(n)) = 2*rad(n) MATHEMATICA rad[n_] := Times @@ Transpose[FactorInteger[n]][[1]]; Select[Range[1000000], rad[DivisorSigma[1, #]] == 2*rad[#] &] PROG (PARI) rad(n)= my(p=factor(n)[, 1]); prod(i=1, length(p), p[i]); isok(n) = rad(sigma(n)) == 2*rad(n); \\ Michel Marcus, Feb 28 2014 CROSSREFS Cf. A000203 (sigma), A007947 (rad). Sequence in context: A159201 A211680 A212610 * A157734 A210102 A061073 Adjacent sequences:  A238327 A238328 A238329 * A238331 A238332 A238333 KEYWORD nonn AUTHOR T. D. Noe, Feb 27 2014 EXTENSIONS More terms from Michel Marcus, Feb 28 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.

Last modified June 24 22:15 EDT 2019. Contains 324337 sequences. (Running on oeis4.)