A155721 - OEIS

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A155721

Positions of parity change in A033035.

4, 20, 84, 340, 1364, 5460, 21844, 87380, 349524, 1398100, 5592404, 22369620, 89478484, 357913940, 1431655764, 5726623060, 22906492244, 91625968980, 366503875924, 1466015503700, 5864062014804, 23456248059220, 93824992236884

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OFFSET

1,1

COMMENTS

Numbers n such that A033035(n)=(7/8)*(9^n - 1)=7*A002452(n).

LINKS

Table of n, a(n) for n=1..23.

FORMULA

a(n=1,2..)=(4/3)*(4^n-1)=A080674(n).

a(n) = 5*a(n-1) - 4*a(n-2) for n > 2. G.f.: 4*x/((x - 1)*(4*x - 1)). - Chai Wah Wu, Aug 30 2019

EXAMPLE

A033035(n=1..4) all are odd, then A033035(n=5..20) all are even, then A033035(n=21..84) all are odd, then A033035(n=85..340) all are even, etc.

CROSSREFS

A002452, A033035, A080674.

Sequence in context: A003489 A167682 A246574 * A084240 A080674 A246936

Adjacent sequences: A155718 A155719 A155720 * A155722 A155723 A155724

KEYWORD

nonn

AUTHOR

Zak Seidov, Jan 25 2009

STATUS

approved