The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A076230 Numbers k such that sigma_2(k)/k and sigma_4(k)/k are integers. 2
 1, 84, 435708, 986076, 1441188, 6066396, 7407036, 16763292, 18735444, 78863148, 260855028, 318502548, 1340673516, 3391115364, 10829086632, 45076171140, 45582899544, 57648961188, 77314641768, 128293717860, 149098104540, 174975241896, 440359518060, 461191689504 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Giovanni Resta, Table of n, a(n) for n = 1..41 (terms < 5*10^12) EXAMPLE For k = 6066396, sigma_2(k)/k = 9156979, sigma_4(k)/k = 241153415598179286943. MATHEMATICA Select[Range[10^7], And @@ Divisible[DivisorSigma[{2, 4}, #], #] &] (* Amiram Eldar, Jan 20 2020 *) PROG (PARI) isok(n) = !(sigma(n, 2) % n) && !(sigma(n, 4) % n); \\ Michel Marcus, Aug 28 2019 (MAGMA) [n: n in [1..10000000]|IsIntegral(DivisorSigma(2, n)/n) and IsIntegral(DivisorSigma(4, n)/n)]; // Marius A. Burtea, Aug 28 2019 CROSSREFS Intersection of A046762 and A046764. Cf. A001157, A001159. Sequence in context: A289557 A202580 A292196 * A118076 A056746 A111194 Adjacent sequences:  A076227 A076228 A076229 * A076231 A076232 A076233 KEYWORD nonn AUTHOR Labos Elemer, Oct 03 2002 EXTENSIONS More terms from T. D. Noe, Apr 11 2006 a(11)-a(12) from Michel Marcus, Aug 28 2019 a(13)-a(18) from Amiram Eldar, Jan 20 2020 a(19)-a(24) from Giovanni Resta, Jan 21 2020 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 21 16:47 EDT 2021. Contains 345365 sequences. (Running on oeis4.)