OFFSET
1,1
COMMENTS
From Donovan Johnson, Jan 25 2009: (Start)
a(14) <= 45780008337005062835;
a(15) <= 3909612711980232366109;
a(16) <= 261944051702675568529303. (End)
FORMULA
a(n) = Min{x; sigma(x)/2x < 1 and A001221(x) = n}.
EXAMPLE
For n=5: a(5) = 36465 = 3*5*11*13*17; sigma(36465) = 72576 < 72930 = 2*sigma(a(5)).
MATHEMATICA
q[x_] := Apply[Times, Table[Prime[w], {w, 1, x}]]; q[0]=1; Do[s=DivisorSigma[1, n]; If[Greater[2*n, s]&&Equal[lf[n], j]&& Equal[fl, 1], Print[{n, {s, 2*n}, j}]; fl=0], {n, q[j], q[j+2]}], {j, 1, 6}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer, Sep 01 2003
EXTENSIONS
a(6) corrected and a(7)-a(13) from Donovan Johnson, Jan 25 2009
a(14)-a(17) from Jon E. Schoenfield, Jul 08 2018
STATUS
approved