login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo

Please make a donation to keep the OEIS running. We are now in our 56th year. In the past year we added 10000 new sequences and reached almost 9000 citations (which often say "discovered thanks to the OEIS").
Other ways to donate

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A287381 a(n) = a(n-1) + 2*a(n-2) - a(n-3), where a(0) = 2, a(1) = 4, a(2) = 7. 4
2, 4, 7, 13, 23, 42, 75, 136, 244, 441, 793, 1431, 2576, 4645, 8366, 15080, 27167, 48961, 88215, 158970, 286439, 516164, 930072, 1675961, 3019941, 5441791, 9805712, 17669353, 31838986, 57371980, 103380599, 186285573, 335674791, 604865338, 1089929347 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

COMMENTS

Conjecture:  a(n) is the number of letters (0's and 1's) in the n-th iteration of the mapping 00->0010, 1->10, starting with 00; see A287931.

LINKS

Clark Kimberling, Table of n, a(n) for n = 0..2000

Index entries for linear recurrences with constant coefficients, signature (1, 2, -1).

FORMULA

a(n) = a(n-1) + 2*a(n-2) - a(n-3), where a(0) = 2, a(1) = 4, a(2) = 7.

G.f.: (2 + 2*x - x^2)/(1 - x - 2*x^2 + x^3).

MATHEMATICA

LinearRecurrence[{1, 2, -1}, {2, 4, 7}, 40]

CROSSREFS

Cf. A287931, A078038 (signed version).

Sequence in context: A303666 A260917 A165648 * A078038 A190502 A048888

Adjacent sequences:  A287378 A287379 A287380 * A287382 A287383 A287384

KEYWORD

nonn,easy

AUTHOR

Clark Kimberling, Jun 07 2017

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified November 28 14:27 EST 2020. Contains 338724 sequences. (Running on oeis4.)