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!)
A303995 Numbers whose sum of divisors is the fifth power of one of their divisors. 6
1, 3210, 3498, 3882, 6453804, 7873684, 7943640, 8028120, 8099880, 9112230, 9561990, 10079430, 182626920, 192651480, 196192920, 199939320, 200271960, 201632760, 203289240, 206367480, 206645880, 207815160, 208955160, 210368760, 210406680, 210717720, 211645560 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Subset of A019423.

LINKS

Table of n, a(n) for n=1..27.

EXAMPLE

Divisors of 3210 are 1, 2, 3, 5, 6, 10, 15, 30, 107, 214, 321, 535, 642, 1070, 1605, 3210 and their sum is 7776 = 6^5.

MAPLE

with(numtheory): P:=proc(q) local a, k, n;

for n from 1 to q do a:=sort([op(divisors(n))]);

for k from 1 to nops(a) do if sigma(n)=a[k]^5 then print(n); break; fi; od; od; end: P(10^9);

MATHEMATICA

Select[Range[10^4], IntegerQ[t = DivisorSigma[1, #]^(1/5)] && Mod[#, t] == 0 &] (* Giovanni Resta, May 04 2018 *)

PROG

(PARI) isok(n) = (n==1) || (ispower(s=sigma(n), 5) && !(n % sqrtnint(s, 5))); \\ Michel Marcus, May 05 2018

CROSSREFS

Cf. A000203, A019423, A303123, A303993, A303994, A303996.

Sequence in context: A236252 A232262 A048255 * A091329 A261241 A020414

Adjacent sequences:  A303992 A303993 A303994 * A303996 A303997 A303998

KEYWORD

nonn

AUTHOR

Paolo P. Lava, May 04 2018

EXTENSIONS

a(13)-a(27) from Giovanni Resta, May 04 2018

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 8 12:31 EDT 2020. Contains 333314 sequences. (Running on oeis4.)