|
|
A223611
|
|
Numbers k whose abundance is 20: sigma(k) - 2*k = 20.
|
|
4
|
|
|
176, 1376, 3230, 3770, 6848, 114256, 125696, 544310, 561824, 740870, 2075648, 4199030, 4607296, 8436950, 33468416, 134045696, 199272950, 624032630, 1113445430, 1550860550, 85905593344, 2199001235456, 35184284008448, 10805836895078390, 103285638050111990
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,1
|
|
COMMENTS
|
a(22) > 10^12.
Any term x of this sequence can be combined with any term y of A223607 to satisfy the property (sigma(x)+sigma(y))/(x+y) = 2, which is a necessary (but not sufficient) condition for two numbers to be amicable. - Timothy L. Tiffin, Sep 13 2016
Every number of the form 2^(j-1)*(2^j - 21), where 2^j - 21 is prime, is a term. - Jon E. Schoenfield, Jun 02 2019
|
|
LINKS
|
|
|
EXAMPLE
|
For k = 544310, sigma(k) - 2*k = 20.
|
|
MATHEMATICA
|
Select[Range[1, 10^8], DivisorSigma[1, #] - 2 # == 20 &] (* Vincenzo Librandi, Sep 14 2016 *)
|
|
PROG
|
(PARI) for(n=1, 10^8, if(sigma(n)-2*n==20, print1(n ", ")))
(Magma) [n: n in [1..9*10^6] | (SumOfDivisors(n)-2*n) eq 20]; // Vincenzo Librandi, Sep 14 2016
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
EXTENSIONS
|
|
|
STATUS
|
approved
|
|
|
|