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 A003154 Centered 12-gonal numbers, or centered dodecagonal numbers: numbers of the form 6*k*(k-1) + 1. (Formerly M4893) 79
 1, 13, 37, 73, 121, 181, 253, 337, 433, 541, 661, 793, 937, 1093, 1261, 1441, 1633, 1837, 2053, 2281, 2521, 2773, 3037, 3313, 3601, 3901, 4213, 4537, 4873, 5221, 5581, 5953, 6337, 6733, 7141, 7561, 7993, 8437, 8893, 9361, 9841, 10333, 10837, 11353, 11881, 12421 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Binomial transform of [1, 12, 12, 0, 0, 0, ...]. Narayana transform (A001263) of [1, 12, 0, 0, 0, ...]. - Gary W. Adamson, Dec 29 2007 Numbers k such that 6*k+3 is a square, these squares are given in A016946. - Gary Detlefs and Vincenzo Librandi, Aug 08 2010 Odd numbers of the form floor(n^2/6). - Juri-Stepan Gerasimov, Jul 27 2011 Bisection of A032528. - Omar E. Pol, Aug 20 2011 Sequence found by reading the line from 1, in the direction 1, 13, ..., in the square spiral whose vertices are the generalized pentagonal numbers A001318. Opposite numbers to the members of A033581 in the same spiral. - Omar E. Pol, Sep 08 2011 The digital root has period 3 (1, 4, 1) (A146325), the same digital root as the centered triangular numbers A005448(n). - Peter M. Chema, Dec 20 2023 REFERENCES M. Gardner, Time Travel and Other Mathematical Bewilderments. Freeman, NY, 1988, p. 20. N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS T. D. Noe, Table of n, a(n) for n = 1..1000 John Elias, Illustration: Star Configurations on the Zero-Centered Hexagonal Number Spiral John Elias, Illustration: Star Configurations on the Zero-Centered Square and Hexagonal Number Spirals John Elias, Illustration: Generalized Pentagonal and Octagonal Numbers in the Star-Crossed Configurations John Elias, Illustration: Generalized Pentagonal and Octagonal Integration in Centered 9-gonal Triangles M. Gardner and N. J. A. Sloane, Correspondence, 1973-74 Marco Matone and Roberto Volpato, Vector-Valued Modular Forms from the Mumford Form, Schottky-Igusa Form, Product of Thetanullwerte and the Amazing Klein Formula, arXiv:1102.0006 [math.AG], 2011-2012, c_n. Simon Plouffe, Approximations de séries génératrices et quelques conjectures, Dissertation, Université du Québec à Montréal, 1992; arXiv:0911.4975 [math.NT], 2009. Simon Plouffe, 1031 Generating Functions, Appendix to Thesis, Montreal, 1992 Amelia C. Sparavigna, Groupoid of OEIS A003154 numbers (star numbers or centered dodecagonal numbers, Politecnico di Torino, Repository istituzionale (2019). Amelia Carolina Sparavigna, Groupoid of OEIS A003154 Numbers (star numbers or centered dodecagonal numbers), Department of Applied Science and Technology, Politecnico di Torino (Italy, 2019). Amelia Carolina Sparavigna, Generalized Sum of Stella Octangula Numbers, Politecnico di Torino (Italy, 2021). Leo Tavares, Illustration: Twin Hexagons Leo Tavares, Illustration: Diamond Rays Eric Weisstein's World of Mathematics, Star Number Index entries for linear recurrences with constant coefficients, signature (3,-3,1). Index entries for sequences related to centered polygonal numbers FORMULA G.f.: x*(1+10*x+x^2)/(1-x)^3. Simon Plouffe in his 1992 dissertation a(n) = 1 + Sum_{j=0..n} (12*j). E.g., a(2)=37 because 1 + 12*0 + 12*1 + 12*2 = 37. - _Xavier Acloque_, Oct 06 2003 a(n) = numerator in B_2(x) = (1/2)x^2 - (1/2)x + 1/12 = Bernoulli polynomial of degree 2. - Gary W. Adamson, May 30 2005 a(n) = 12*(n-1) + a(n-1), with n>1, a(1)=1. - Vincenzo Librandi, Aug 08 2010 a(n) = A049598(n-1) + 1. - Omar E. Pol, Oct 03 2011 Sum_{n>=1} 1/a(n) = A306980 = Pi * tan(Pi/(2*sqrt(3))) / (2*sqrt(3)). - Vaclav Kotesovec, Jul 23 2019 From Amiram Eldar, Jun 21 2020: (Start) Sum_{n>=1} a(n)/n! = 7*e - 1. Sum_{n>=1} (-1)^n * a(n)/n! = 7/e - 1. (End) a(n) = 2*A003215(n-1) - 1. - Leo Tavares, Jul 30 2021 E.g.f.: exp(x)*(1 + 6*x^2) - 1. - Stefano Spezia, Aug 19 2022 EXAMPLE From Omar E. Pol, Aug 21 2011: (Start) 1. Classic illustration of initial terms of the star numbers: . . o . o o . o o o o o o o o . o o o o o o o o o o . o o o o o o o o o . o o o o o o o o o o . o o o o o o o o . o o . o . . 1 13 37 . 2. Alternative illustration of initial terms using n-1 concentric hexagons around a central element: . . o o o o o . o o . o o o o o o o o . o o o o o o . o o o o o o o o o . o o o o o o . o o o o o o o o . o o . o o o o o (End) MAPLE A003154:=n->6*n*(n-1) + 1: seq(A003154(n), n=1..100); # Wesley Ivan Hurt, Oct 23 2017 MATHEMATICA FoldList[#1 + #2 &, 1, 12 Range@50] (* Robert G. Wilson v *) LinearRecurrence[{3, -3, 1}, {1, 13, 37}, 50] (* Harvey P. Dale, Jul 18 2016 *) 12*Binomial[Range[50], 2] + 1 (* G. C. Greubel, Jul 23 2019 *) PROG (PARI) a(n)=6*n*(n-1)+1 \\ Charles R Greathouse IV, Nov 20 2012 (J) ([: >: 6 * ] * <:) i.1000 NB. Stephen Makdisi, May 06 2018 (Magma) [12*Binomial(n, 2)+1: n in [1..50]]; // G. C. Greubel, Jul 23 2019 (GAP) List([1..50], n-> 12*Binomial(n, 2)+1 ); # G. C. Greubel, Jul 23 2019 (Python) print([6*n*(n-1)+1 for n in range(1, 47)]) # Michael S. Branicky, Jan 13 2021 CROSSREFS Cf. A001263, A001318, A003215, A007588, A016946, A032528, A033581, A049598, A056827, A306980. Row 4 of A257565. Cf. A000217, A005448, A016754, A146325. Sequence in context: A247867 A113601 A158864 * A083577 A155285 A155262 Adjacent sequences: A003151 A003152 A003153 * A003155 A003156 A003157 KEYWORD nonn,easy,nice AUTHOR N. J. A. Sloane EXTENSIONS More terms from Michael Somos STATUS approved

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Last modified February 27 21:03 EST 2024. Contains 370378 sequences. (Running on oeis4.)