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 A003010 A Lucas-Lehmer sequence: a(0) = 4; for n>0, a(n) = a(n-1)^2 - 2. (Formerly M3494) 36
 4, 14, 194, 37634, 1416317954, 2005956546822746114, 4023861667741036022825635656102100994, 16191462721115671781777559070120513664958590125499158514329308740975788034 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS Albert Beiler states (page 228 of Recreations in the Theory of Numbers): D. H. Lehmer modified Lucas's test to the relatively simple form: If and only if 2^n-1 divides a(n-2) then 2^n-1 is a prime, otherwise it is composite. Since 2^3 - 1 is a factor of a(1) = 14, 2^3 - 1 = 7 is a prime. - Gary W. Adamson, Jun 07 2003 a(n) - a(n-1) divides a(n+1) - a(n). - Thomas Ordowski, Dec 24 2016 REFERENCES A. H. Beiler, Recreations in the Theory of Numbers, Dover, NY, 1964, p. 228. L. E. Dickson, History of the Theory of Numbers. Carnegie Institute Public. 256, Washington, DC, Vol. 1, 1919; Vol. 2, 1920; Vol. 3, 1923, see vol. 1, p. 399. Lehmer, Derrick Henry. "On Lucas's test for the primality of Mersenne's numbers." Journal of the London Mathematical Society 1.3 (1935): 162-165. See page 162. N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS N. J. A. Sloane, Table of n, a(n) for n = 0..10 A. V. Aho and N. J. A. Sloane, Some doubly exponential sequences, Fib. Quart., 11 (1973), 429-437. Larry Ericksen, Primality Testing and Prime Constellations, Šiauliai Mathematical Seminar, Vol. 3 (11), 2008. J. S. Hall, A remark on the primeness of Mersenne numbers, J. London Math. Soc. 28, (1953). 285-287. D. H. Lehmer. Mathematical Reviews.  Review of: Hall, James S. A remark on the primeness of Mersenne numbers. (1953) [Annotated scanned copy] P. Liardet and P. Stambul, Séries d'Engel et fractions continuées, Journal de Théorie des Nombres de Bordeaux 12 (2000), 37-68. J. Shallit, An interesting continued fraction, Math. Mag., 48 (1975), 207-211. [Annotated scanned copy] P. Vellucci, A. M. Bersani, The class of Lucas-Lehmer polynomials, arXiv preprint arXiv:1603.01989 [math.CA], 2016. Pierluigi Vellucci, A. M. Bersani, New formulas for pi involving infinite nested square roots and Gray code, arXiv preprint arXiv:1606.09597 [math.NT], 2016 (The OEIS is cited in version 1, but has been dropped from version 4.) Eric Weisstein's World of Mathematics, Lucas-Lehmer Test. Wikipedia, Engel Expansion FORMULA a(n) = ceiling((2 + sqrt(3))^(2^n)). - Benoit Cloitre, Nov 30 2002 More generally, if u(0) = z, integer > 2 and u(n) = a(n-1)^2 - 2 then u(n) = ceiling(c^(2^n)) where c = (1/2)*(z+sqrt(z^2-4)) is the largest root of x^2 - zx + 1 = 0. - Benoit Cloitre, Dec 03 2002 a(n) = (2+sqrt(3))^(2^n) + (2-sqrt(3))^(2^n). - John Sillcox (johnsillcox(AT)hotmail.com), Sep 20 2003 a(n) = ceiling(tan(5*Pi/12)^(2^n)). Note: 5*Pi/12 radians is 75 degrees. - Jason M. Follas (jasonfollas(AT)hotmail.com), Jan 16 2004 Sum_{n >= 0} 1/( Product_{k = 0..n} a(k) ) = 2 - sqrt(3). - Paul D. Hanna, Aug 11 2004 From Ulrich Sondermann, Sep 04 2006: (Start) To generate the n-th number in the sequence: let x = 2^(n-1), a = 2, b = sqrt(3). Take every other term of the binomial expansion (a+b)^x times 2. E.g., for the 4th term: x = 2^(4-1) = 8, the binomial expansion is: a^8 + 7a^7 b + 28a^6 b^2 + 56a^5 b^3 + 70a^4 b^4 + 56a^3 b^5 + 28a^2 b^6 + 7a b^7 + b^8, every other term times 2: 2(a^8 + 28a^6 b^2 + 70a^4 b^4 + 28a^2 b^6 + b^8) = 2(256 + (28)(64)(3) + (70)(16)(9) + (28)(4)(27) + 81) = 2(18817) = 37634. (End) a(n) = 2*cosh( 2^(n-1)*log(sqrt(3)+2) ) For n > 0, a(n) = 2 + 3 * 4^n * (Product_{k=0..n-2} (a(k)/2))^2, where a(k)/2 = A002812(k) is a coprime sequence. - M. F. Hasler, Mar 09 2007 a(n) = A003500(2^n). - John Blythe Dobson, Oct 28 2007 a(n) = 2*T(2^n,2) where T(n,x) is the Chebyshev polynomial of the first kind. - Leonid Bedratyuk, Mar 17 2011 Engel expansion of 2 - sqrt(3). Thus 2 - sqrt(3) = 1/4 + 1/(4*14) + 1/(4*14*194) + ... as noted by Hanna above. See Liardet and Stambul. Cf. A001566, A003423 and A003487. - Peter Bala, Oct 31 2012 From Peter Bala, Nov 11 2012: (Start) 2*sqrt(3)/5 = Product_{n = 0..inf} (1 - 1/a(n)). sqrt(3) = Product_{n = 0..inf} (1 + 2/a(n)). a(n) - 1 = A145503(n+1). a(n) = 2*A002812(n). (End) a(n+1) - a(n) = a(n)^2 - a(n-1)^2. - Thomas Ordowski, Dec 24 2016 MAPLE a := n-> if n>0 then a(n-1)^2-2 else 4 fi: 'a(i)' \$ i=0..9; # M. F. Hasler, Mar 09 2007 a := n-> simplify(2*ChebyshevT(2^n, 2), 'ChebyshevT'): seq(a(n), n=0..7); MATHEMATICA seqLucasLehmer[0] = 4; seqLucasLehmer[n_] := seqLucasLehmer[n - 1]^2 - 2; Array[seqLucasLehmer, 8, 0] (* Robert G. Wilson v, Jun 28 2012 *) PROG (PARI) a(n)=if(n, a(n-1)^2-2, 4) vector(10, i, a(i-1)) \\ M. F. Hasler, Mar 09 2007 (MAGMA) [n le 1 select 4 else Self(n-1)^2-2: n in [1..10]]; // Vincenzo Librandi, Aug 24 2015 CROSSREFS Cf. A001566 (starting with 3), A003423 (starting with 6), A003487 (starting with 5). Cf. A002812, A145503. Sequence in context: A129224 A129225 A129226 * A118770 A226943 A292708 Adjacent sequences:  A003007 A003008 A003009 * A003011 A003012 A003013 KEYWORD nonn AUTHOR EXTENSIONS One more term from Thomas A. Rockwell (LlewkcoRAT(AT)aol.com), Jan 18 2005 STATUS approved

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Last modified December 11 15:03 EST 2018. Contains 318049 sequences. (Running on oeis4.)