OFFSET
1,1
COMMENTS
108927 is the smallest odd term of this sequence.
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..100
EXAMPLE
24 is in the sequence because 24 = 2^3*3 and sum of proper divisors of 24 is 1 + 2 + 3 + 4 + 6 + 8 + 12 = 36 = 2^2*3^2 while sigma(24) = 60 is divisible by 5.
MATHEMATICA
Select[Range[1500000], And[UnsameQ @@ {#1, #2}, SameQ @@ {#1, #3}] & @@ Map[FactorInteger[#][[All, 1]] &, {#1, #2, #2 - #1} & @@ {#, DivisorSigma[1, #]}] &] (* Michael De Vlieger, Aug 02 2017 *)
PROG
(PARI) rad(n) = factorback(factorint(n)[, 1]);
isok(n) = rad(sigma(n)-n)==rad(n) && rad(sigma(n))!=rad(n);
CROSSREFS
KEYWORD
nonn
AUTHOR
Altug Alkan, Aug 02 2017
STATUS
approved