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 A002042 a(n) = 7*4^n. 12
 7, 28, 112, 448, 1792, 7168, 28672, 114688, 458752, 1835008, 7340032, 29360128, 117440512, 469762048, 1879048192, 7516192768, 30064771072, 120259084288, 481036337152, 1924145348608, 7696581394432, 30786325577728, 123145302310912, 492581209243648 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS Subsequence of A000069, the odious numbers. - Reinhard Zumkeller, Aug 26 2007 A rectangular prism with edge lengths 2^n, 2^(n+1) and 2^(n+2) has a surface area 2* (2^n*2^(n+1) + 2^(n+1)*2^(n+2) + 2^n*2^(n+2)) which equals 4*a(n). - J. M. Bergot, Aug 07 2013 x = A306472(n) and y = a(n) satisfy the Lebesgue-Ramanujan-Nagell equation x^2 + 3^(6*n+1) = 4*y^3 (see Theorem 2.1 in Chakraborty, Hoque and Sharma). - Stefano Spezia, Feb 18 2019 LINKS Vincenzo Librandi, Table of n, a(n) for n = 0..500 K. Chakraborty, A. Hoque, R. Sharma, Complete solutions of certain Lebesgue-Ramanujan-Nagell type equations, arXiv:1812.11874 [math.NT], 2018. Tanya Khovanova, Recursive Sequences Index entries for linear recurrences with constant coefficients, signature (4). FORMULA From Philippe Deléham, Nov 23 2008: (Start) a(n) = 4*a(n-1), n > 0, with a(0) = 7. G.f.: 7/(1-4*x). (End) a(n) = 7*A000302(n). - Michel Marcus, Jun 24 2015 E.g.f.: 7*exp(4*x). - G. C. Greubel, Feb 18 2019 MATHEMATICA 7*4^Range[0, 100] (* Vladimir Joseph Stephan Orlovsky, Jun 09 2011 *) CoefficientList[Series[7/(1-4x), {x, 0, 33}], x] (* Vincenzo Librandi, Jun 25 2015 *) PROG (MAGMA) [7*4^n: n in [0..30]]; // Vincenzo Librandi, May 31 2011 (PARI) a(n)=7<<(2*n) \\ Charles R Greathouse IV, Apr 17 2012 (Sage) [7*4^n for n in (0..30)] # G. C. Greubel, Feb 18 2019 CROSSREFS First differences of A083597. Bisection of A005009. Cf. A306472 (37*27^n), A009971 (27^n), A000302 (4^n), A000290 (n^2), A000578 (n^3). Sequence in context: A243150 A026642 A200467 * A200666 A207098 A037597 Adjacent sequences:  A002039 A002040 A002041 * A002043 A002044 A002045 KEYWORD nonn,easy AUTHOR STATUS approved

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Last modified October 23 07:05 EDT 2019. Contains 328335 sequences. (Running on oeis4.)