The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A070039 Sum of divisors of n that are smaller than sqrt(n). 42
 0, 1, 1, 1, 1, 3, 1, 3, 1, 3, 1, 6, 1, 3, 4, 3, 1, 6, 1, 7, 4, 3, 1, 10, 1, 3, 4, 7, 1, 11, 1, 7, 4, 3, 6, 10, 1, 3, 4, 12, 1, 12, 1, 7, 9, 3, 1, 16, 1, 8, 4, 7, 1, 12, 6, 14, 4, 3, 1, 21, 1, 3, 11, 7, 6, 12, 1, 7, 4, 15, 1, 24, 1, 3, 9, 7, 8, 12, 1, 20, 4, 3, 1, 23, 6, 3, 4, 15, 1, 26, 8, 7, 4, 3, 6 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,6 LINKS G. C. Greubel, Table of n, a(n) for n = 1..5000 FORMULA a(n) = sigma(n) - A070038(n). a(n) = Sum_{n>=1} n*x^(n^2+n)/(1-x^n). - Vladeta Jovovic, Feb 09 2005 EXAMPLE a(96) = 1+2+3+4+6+8+12 = 36; a(225) = 1+3+5+9 = 18. MATHEMATICA di[x_] := Divisors[x] lds[x_] := Ceiling[DivisorSigma[0, x]/2] rd[x_] := Reverse[Divisors[x]] td[x_] := Table[Part[rd[x], w], {w, 1, lds[x]}] sud[x_] := Apply[Plus, td[x]] Table[DivisorSigma[1, w]-sud[w], {w, 1, 128}] Table[DivisorSum[n, #&, #

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

Last modified May 5 19:06 EDT 2021. Contains 343573 sequences. (Running on oeis4.)