A304383 a(n) = 36*2^n - 5 (n>=1).

67, 139, 283, 571, 1147, 2299, 4603, 9211, 18427, 36859, 73723, 147451, 294907, 589819, 1179643, 2359291, 4718587, 9437179, 18874363, 37748731, 75497467, 150994939, 301989883, 603979771, 1207959547, 2415919099, 4831838203, 9663676411, 19327352827, 38654705659, 77309411323

Offset

1,1

Comments

a(n) is the number of edges in the molecular graph NS2[n], defined pictorially in the Ashrafi et al. reference (Fig. 2, where NS2[2] is shown).

Links

Colin Barker, Table of n, a(n) for n = 1..1000

Ali Reza Ashrafi and Parisa Nikzad, Kekulé index and bounds of energy for nanostar dendrimers, Digest J. of Nanomaterials and Biostructures, 4, No. 2, 2009, 383-388.

Index entries for linear recurrences with constant coefficients, signature (3,-2).

Formula

From Colin Barker, May 14 2018: (Start)

G.f.: x*(67 - 62*x) / ((1 - x)*(1 - 2*x)).

a(n) = 3*a(n-1) - 2*a(n-2) for n>2.

(End)

Maple

seq(36*2^n-5, n = 1 .. 40);

Prog

(GAP) List([1..40], n->36*2^n-5); # Muniru A Asiru, May 13 2018
(PARI) Vec(x*(67 - 62*x) / ((1 - x)*(1 - 2*x)) + O(x^40)) \\ Colin Barker, May 14 2018

Crossrefs

Cf. A304382.

Sequence in context: A142097 A106755 A320876 * A238083 A118200 A163303

Adjacent sequences: A304380 A304381 A304382 * A304384 A304385 A304386

Keyword

nonn,easy

Author

Emeric Deutsch, May 13 2018

Status

approved