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A099942 Start with 1, then alternately double or add 2. 1
1, 2, 4, 8, 10, 20, 22, 44, 46, 92, 94, 188, 190, 380, 382, 764, 766, 1532, 1534, 3068, 3070, 6140, 6142, 12284, 12286, 24572, 24574, 49148, 49150, 98300, 98302, 196604, 196606, 393212, 393214, 786428, 786430, 1572860, 1572862, 3145724, 3145726 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 0..5000

FORMULA

a(0)=1; for n > 0, a(n) = a(n-1)*(1 + n mod 2) + 2*((n+1) mod 2).

G.f.: (2*x^3 + x^2 + 2*x + 1)/(2*x^4 - 3*x^2 + 1)

3*2^ceiling(n/2) + (-1)^n - 3. - Ralf Stephan, Dec 04 2004

a(2*n) = A033484(n).

a(n-1) + a(n) = A061776(n) for n > 0.

PROG

(PARI) print1(a=1, ", "); for(n=1, 20, print1(a=2*a, ", ", a=a+2, ", "))

(MAGMA) [3*2^Ceiling(n/2) + (-1)^n - 3: n in [0..50]]; // Vincenzo Librandi, Aug 17 2011

CROSSREFS

Cf. A033484, A061776, A075427, A083416.

Sequence in context: A095726 A173816 A185400 * A033092 A177909 A004655

Adjacent sequences:  A099939 A099940 A099941 * A099943 A099944 A099945

KEYWORD

nonn,easy

AUTHOR

N. J. A. Sloane, Nov 12 2004

EXTENSIONS

Edited and extended by Klaus Brockhaus, Nov 13 2004

STATUS

approved

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Last modified April 17 11:46 EDT 2014. Contains 240635 sequences.