OFFSET
1,1
COMMENTS
Aursukaree & Pongsriiam prove that 1521 is the only odd term with at most two distinct prime factors.
LINKS
Saralee Aursukaree and Prapanpong Pongsriiam, On Exactly 3-Deficient-Perfect Numbers, arXiv:2001.06953 [math.NT], 2020.
EXAMPLE
130 is an exactly 3-deficient-perfect number with d1=1, d2=2 and d3=5: sigma(130) = 252 = 2*130 - (1+2+5).
MATHEMATICA
def3[n_] := Catch@ Block[{s = 2*n - DivisorSigma[1, n], d}, If[s > 0, d = Most@ Divisors@ n; Do[If[s == d[[i]] + d[[j]] + d[[k]], Throw@ True], {i, 3, Length@ d}, {j, i-1}, {k, j-1}]; False]]; Select[ Range[6000], def3] (* Giovanni Resta, Jan 23 2020 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Michel Marcus, Jan 23 2020
EXTENSIONS
More terms from Giovanni Resta, Jan 23 2020
STATUS
approved