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 A016791 a(n) = (3*n + 2)^3. 14
 8, 125, 512, 1331, 2744, 4913, 8000, 12167, 17576, 24389, 32768, 42875, 54872, 68921, 85184, 103823, 125000, 148877, 175616, 205379, 238328, 274625, 314432, 357911, 405224, 456533, 512000, 571787, 636056, 704969, 778688, 857375, 941192 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS Also the perfect cubes with digital root 8. [Proof: perfect cubes are either of the form (3n)^3 or of the form (3n+1)^3 or of the form (3n+2)^3. These subsets have digital root 9, 1 and 8 respectively.] - R. J. Mathar, Oct 02 2008 REFERENCES Amarnath Murthy, Fabricating a perfect cube with a given valid digit sum (to be published) LINKS Harry J. Smith, Table of n, a(n) for n = 0..1000 Index entries for linear recurrences with constant coefficients, signature (4,-6,4,-1). FORMULA a(n) = (3*n-1)^3 = A016789(n-1)^3. - Nathaniel Johnston, May 04 2011 G.f.: (8+93*x+60*x^2+x^3)/(1-4*x+6*x^2-4*x^3+x^4). - Colin Barker, Jan 02 2012 a(0)=8, a(1)=125, a(2)=512, a(3)=1331, a(n)=4*a(n-1)-6*a(n-2)+4*a(n-3)-a(n-4). - Harvey P. Dale, Feb 20 2013 Sum_{n>=0} 1/a(n) = -2*Pi^3 / (81*sqrt(3)) + 13*zeta(3)/27. - Amiram Eldar, Oct 02 2020 EXAMPLE a(4) = (3*4 + 2)^3 = 2744. a(8) = (3*8 + 2)^3 = 17576. MATHEMATICA (3*Range[0, 40]+2)^3 (* or *) LinearRecurrence[{4, -6, 4, -1}, {8, 125, 512, 1331}, 40] (* Harvey P. Dale, Feb 20 2013 *) PROG (PARI) { for (n=0, 1000, write("b016791.txt", n, " ", (3*n + 2)^3) ) } \\ Harry J. Smith, Jul 18 2009 (PARI) { b=0; for (n=1, 1000, until (s==8, b++; s=b^3; s-=9*(s\9)); write("b016791.txt", n, " ", b^3) ) } \\ Harry J. Smith, Jul 18 2009 CROSSREFS Cf. A054966, A016779, A073636. Sequence in context: A065082 A053058 A050803 * A061103 A264143 A110272 Adjacent sequences: A016788 A016789 A016790 * A016792 A016793 A016794 KEYWORD nonn,easy AUTHOR N. J. A. Sloane EXTENSIONS More terms from Harry J. Smith, Jul 18 2009 First digital root in proof in comment line corrected. - Ant King, May 01 2013 STATUS approved

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Last modified December 6 13:45 EST 2023. Contains 367601 sequences. (Running on oeis4.)