The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A336672 Unitary barely 3-deficient numbers: numbers m such that usigma(k)/k < usigma(m)/m < 3 for all numbers k < m, where usigma is the sum of unitary divisors function (A034448). 1
 1, 2, 6, 30, 210, 2310, 110670, 182910, 898590, 22851570, 26266170, 45255210, 64124970, 265402410, 1374105810, 1631268870 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Unitary 3-deficient numbers are numbers k such that usigma(k) < 3*k, i.e., numbers that are not in A285615. The corresponding values of usigma(m)/m are 1, 1.5, 2, 2.4, 2.742..., 2.992..., ... Are terms squarefree? At some point, do we know that a(n) is divisible by primorial(k) for all n > N(k) for some N(k)? - David A. Corneth, Jul 29 2020 Not all the terms are squarefree. E.g., a(12) = 45255210 is divisible by 11^2. LINKS Table of n, a(n) for n=1..16. MATHEMATICA usigma[1] = 1; usigma[n_] := Times @@ (1 + Power @@@ FactorInteger[n]); s = {}; rm = 0; Do[r = usigma[n]/n; If[r < 3 && r > rm, rm = r; AppendTo[s, n]], {n, 1, 10^5}]; s CROSSREFS The unitary version of A307122. Cf. A034448, A129487, A285615, A302572, A336671. Sequence in context: A359960 A088257 A058694 * A046853 A136351 A071290 Adjacent sequences: A336669 A336670 A336671 * A336673 A336674 A336675 KEYWORD nonn,more AUTHOR Amiram Eldar, Jul 29 2020 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified August 12 13:41 EDT 2024. Contains 375113 sequences. (Running on oeis4.)