OFFSET
1,2
COMMENTS
a(12) > 11*10^5. - Emeric Deutsch, Mar 05 2005
8*10^11 < a(19) <= 2343594361433 = 13^10*17. It seems that the numbers 5^(13*k-3)*13 and 13^(17*k-7)*17, for k > 0, are terms. - Giovanni Resta, Dec 06 2019
EXAMPLE
The divisors of 615 are [615,205,123,41,15,5,3,1] and 1/615+2/205+3/123+4/41+5/15+6/5+7/3+8/1 = 12 is an integer hence 615 is in the sequence.
MATHEMATICA
Select[Range[441000], IntegerQ[Total[Range[DivisorSigma[0, #]]/ Reverse[ Divisors[ #]]]]&] (* Harvey P. Dale, May 23 2019 *)
PROG
(Magma) [k:k in [1..500000]|IsIntegral(&+[m/Reverse(Divisors(k))[m]:m in [1..#Divisors(k)]])]; // Marius A. Burtea, Dec 06 2019
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Benoit Cloitre, Aug 17 2002
EXTENSIONS
More terms from Emeric Deutsch, Mar 05 2005
a(12)-a(17) from Lambert Klasen (lambert.klasen(AT)gmx.net), Jul 15 2005
a(18) from Giovanni Resta, Dec 06 2019
STATUS
approved