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A093357
Number of occurrences of pattern 2-1 after n iterations of morphism A007413.
2
0, 4, 20, 88, 368, 1504, 6080, 24448, 98048, 392704, 1571840, 6289408, 25161728, 100655104, 402636800, 1610579968, 6442385408, 25769672704, 103078952960, 412316336128, 1649266393088, 6597067669504, 26388274872320
OFFSET
1,2
FORMULA
a(1) = 0, a(n) = (3*4^(n-1) - 2^n)/2.
G.f.: 4*x*(1-x)/((1-2*x)*(1-4*x)).
a(1)=0, a(2)=4, a(3)=20, a(n)=6*a(n-1)-8*a(n-2). - Harvey P. Dale, Apr 04 2012
a(n) = 4*A010036(n-2). - R. J. Mathar, Apr 07 2022
MATHEMATICA
Join[{0}, Table[(3*4^(n-1)-2^n)/2, {n, 2, 30}]] (* or *) Join[{0}, LinearRecurrence[{6, -8}, {4, 20}, 30]] (* Harvey P. Dale, Apr 04 2012 *)
PROG
(PARI) a(n)=if(n==1, 0, (3*4^(n-1)-2^n)/2)
CROSSREFS
Sequence in context: A320936 A320937 A196953 * A027156 A017964 A017965
KEYWORD
nonn,easy
AUTHOR
Ralf Stephan, Apr 27 2004
STATUS
approved