This site is supported by donations to The OEIS Foundation. Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A152007 a(n) = (2^phi(3^n)-1)/3^n. 3
 1, 1, 7, 9709, 222399981598543, 24057640120673299065081231814259802792690247621 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS The next term is too large to display. With the exception of 7 there are no primes in this sequence. All numbers in this sequence are squarefree. a(n) is divisible by a(k) for every k < n. The sequence of number of digits of a(n), n >= 1, is 1, 1, 1, 4, 15, 47, 144, 436, 1313, 3946, 11846, 35546, 106648, 319954, 959872, 2879628, 8638896, 25916701, 77750117, 233250368, 699751120,... - Wolfdieter Lang, Feb 21 2014 Each a(n) is by definition the same as the repetend of 1/3^n, viewed as a binary integer. E.g., 1/9 = .000111000111...; consequently a(2) = 000111 (base 2) = 7 (base 10) - Joe Slater, Nov 29 2016 LINKS Vincenzo Librandi, Table of n, a(n) for n = 0..7 W. Lang, On Collatz' Words, Sequences and Trees, arXiv preprint arXiv:1404.2710 [math.NT], 2014  and J. Int. Seq. 17 (2014) # 14.11.7. FORMULA a(n) = (4^(3^(n-1)) - 1)/3^n for n>=1, a(0) = 1, with EulerPhi(1) = 1 = A000010(1). - Wolfdieter Lang, Feb 21 2014 MATHEMATICA Table[(2^EulerPhi[3^n] - 1)/3^n, {n, 0, 10}] PROG (MAGMA) [(2^EulerPhi(3^n)-1)/3^n: n in [0..6]]; // Vincenzo Librandi, Feb 23 2014 (PARI) a(n)=(2^eulerphi(3^n)-1)/3^n \\ Charles R Greathouse IV, Nov 29 2016 CROSSREFS Cf. A008776, A152008, A234039. Sequence in context: A212937 A074489 A067248 * A242773 A131676 A280813 Adjacent sequences:  A152004 A152005 A152006 * A152008 A152009 A152010 KEYWORD nonn AUTHOR Artur Jasinski, Nov 19 2008 EXTENSIONS Edited by N. J. A. Sloane, Nov 28 2008 Offset corrected from Wolfdieter Lang, Feb 21 2014 Definition clarified by Joerg Arndt, Feb 23 2014 STATUS approved

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 November 15 06:11 EST 2019. Contains 329144 sequences. (Running on oeis4.)