OFFSET
1,1
COMMENTS
No further term between 523776 and 4050045000. - R. J. Mathar, Feb 11 2008
a(7) > 10^20, if it exists. - Amiram Eldar, Aug 05 2023
FORMULA
EXAMPLE
a(1) = 66 because 11*(11+1)/2 = 66 and 1+2+3+11+22+33-6 = 66.
MATHEMATICA
admQ[n_] := (ab = DivisorSigma[1, n] - 2 n) > 0 && EvenQ[ab] && ab/2 < n && Divisible[n, ab/2]; Select[Accumulate[Range[1024]], admQ] (* Amiram Eldar, Aug 05 2023 *)
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Jason Earls, Aug 11 2005
STATUS
approved