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A047352 Numbers that are congruent to {0, 2} mod 7. 6
0, 2, 7, 9, 14, 16, 21, 23, 28, 30, 35, 37, 42, 44, 49, 51, 56, 58, 63, 65, 70, 72, 77, 79, 84, 86, 91, 93, 98, 100, 105, 107, 112, 114, 119, 121, 126, 128, 133, 135, 140, 142, 147, 149, 154, 156, 161, 163, 168, 170 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Numbers k such that k^2/7 + k*(k + 1)/14 = k*(3*k + 1)/14 is a nonnegative integer. - Bruno Berselli, Feb 14 2017

LINKS

Table of n, a(n) for n=1..50.

Index entries for linear recurrences with constant coefficients, signature (1,1,-1).

FORMULA

a(n) = 7*n-a(n-1)-12 with a(1)=0. Also: a(n) = a(n-1) + a(n-2) - a(n-3). - Vincenzo Librandi, Aug 05 2010

a(n+1) = Sum_{k>=0} A030308(n,k)*b(k) with b(0)=2 and b(k)=A005009(k-1) for k>0. - Philippe Deléham, Oct 17 2011

G.f. x^2*(2 + 5*x)/((1 + x)*(1 - x)^2). - R. J. Mathar, Dec 04 2011

a(n) = floor((7/3)*floor(3*n/2)). - Clark Kimberling, Jul 04 2012

PROG

(PARI) forstep(n=0, 200, [2, 5], print1(n", ")) \\ Charles R Greathouse IV, Oct 17 2011

CROSSREFS

Sequence in context: A253047 A077470 A205559 * A184400 A074244 A190565

Adjacent sequences:  A047349 A047350 A047351 * A047353 A047354 A047355

KEYWORD

nonn,easy

AUTHOR

N. J. A. Sloane

STATUS

approved

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Last modified May 11 21:35 EDT 2021. Contains 343808 sequences. (Running on oeis4.)