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 A106710 Number of words with n letters from an alphabet of size 26 with at least two equal consecutive letters. 2
 0, 26, 1326, 50726, 1725126, 55009526, 1684153926, 50135658326, 1462218522726, 41984966747126, 1190791264331526, 33440126095275926, 931432109043580326, 25766955599293244726, 708683864685628269126, 19394355959426432653526, 528467641885089690397926 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Colin Barker, Table of n, a(n) for n = 1..706 Index entries for linear recurrences with constant coefficients, signature (51,-650). FORMULA a(n) = 26^n - 26*25^(n - 1). From Colin Barker, Nov 05 2015: (Start) a(n) = 51*a(n-1) - 650*a(n-2) for n>2. G.f.: 26*x^2 / ((1-25*x)*(1-26*x)). (End) From G. C. Greubel, Sep 10 2021: (Start) a(n) = 26*(A009970(n-1) - A009969(n-1)). E.g.f.: exp(26*x) - (26/25)*exp(25*x). (End) EXAMPLE a(3) = 1326 because 26^3 - 26*(25^2) = 1326. MATHEMATICA Table[26*(26^(n-1) -25^(n-1)), {n, 25}] (* G. C. Greubel, Sep 10 2021 *) PROG (PARI) a(n) = 26^n - 26*(25^(n - 1)); \\ Michel Marcus, Aug 14 2013 (PARI) concat(0, Vec(26*x^2/((25*x-1)*(26*x-1)) + O(x^100))) \\ Colin Barker, Nov 05 2015 (Sage) [26*(26^(n-1) - 25^(n-1)) for n in (1..25)] # G. C. Greubel, Sep 10 2021 CROSSREFS Cf. A009969, A009970, Sequence in context: A187463 A160311 A220955 * A114052 A042303 A042300 Adjacent sequences:  A106707 A106708 A106709 * A106711 A106712 A106713 KEYWORD nonn,easy AUTHOR Luca Colucci, May 14 2005 EXTENSIONS More terms from Michel Marcus, Aug 14 2013 STATUS approved

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Last modified July 3 04:37 EDT 2022. Contains 355030 sequences. (Running on oeis4.)