|
|
A332208
|
|
Numbers k such that the squarefree kernel of sigma(k) is equal to the squarefree kernel of 2*k.
|
|
4
|
|
|
6, 28, 120, 135, 270, 496, 672, 891, 1080, 1638, 1782, 3780, 8128, 18600, 20580, 24948, 26208, 30240, 32640, 32760, 35640, 41850, 44226, 55860, 66960, 164640, 167400, 185220, 199584, 200655, 273000, 293760, 307125, 401310, 441936, 446880, 502740, 523776, 544635, 614250, 707616, 802620, 819000, 884520
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,1
|
|
COMMENTS
|
Numbers k such that sigma(k) has the same set of distinct prime factors as 2*k.
Of the first 256 terms 44 are odd, and none occurs in A228058. Compare also to A331752.
|
|
LINKS
|
|
|
FORMULA
|
|
|
MATHEMATICA
|
Select[Range[10^6], SameQ @@ Map[Times @@ FactorInteger[#][[All, 1]] &, {DivisorSigma[1, #], 2 #}] &] (* Michael De Vlieger, Feb 08 2020 *)
|
|
PROG
|
(PARI)
A007947(n) = factorback(factorint(n)[, 1]);
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|