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

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A366662 Sum of the divisors of 9^n-1. 12
 15, 186, 1680, 15876, 123690, 1541568, 8992680, 111757968, 967814400, 9366647892, 62424587520, 852903426816, 4766016364260, 55176998178240, 550081165885440, 4829754617483040, 31725040326819840, 471309320999516160, 2535353780263288800, 33995669076586206864 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Max Alekseyev, Table of n, a(n) for n = 1..690 FORMULA a(n) = sigma(9^n-1) = A000203(A024101(n)). a(n) = A366576(2*n) = A366576(n) * A366578(n) * (2^(4 + A007814(n)) - 1) / (2^(3 + A007814(n)) - 1) / 3. - Max Alekseyev, Jan 07 2024 EXAMPLE a(2)=186 because 9^2-1 has divisors {1, 2, 4, 5, 8, 10, 16, 20, 40, 80}. MAPLE a:=n->numtheory[sigma](9^n-1): seq(a(n), n=1..30); MATHEMATICA DivisorSigma[1, 9^Range[30]-1] CROSSREFS Cf. A024101, A000203, A366660, A366661, A366663. Cf. A075708, A366576, A366603, A366613, A366622, A366634, A366653, A102146, A366684, A366710. Sequence in context: A273654 A079516 A206521 * A240796 A206514 A016207 Adjacent sequences: A366659 A366660 A366661 * A366663 A366664 A366665 KEYWORD nonn AUTHOR Sean A. Irvine, Oct 15 2023 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 September 15 22:11 EDT 2024. Contains 375959 sequences. (Running on oeis4.)