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 A174348 Alternately multiply and divide, with a(1)=3 and a(1)=7. 4

%I

%S 3,7,21,3,63,21,1323,63,83349,1323,110270727,83349,9190954824723,

%T 110270727,1013493270346362783621,9190954824723,

%U 9314970862914194811435918430261983,1013493270346362783621

%N Alternately multiply and divide, with a(1)=3 and a(1)=7.

%H Robert Israel, <a href="/A174348/b174348.txt">Table of n, a(n) for n = 1..32</a>

%F From _Robert Israel_, Dec 05 2016: (Start)

%F a(2k) = a(2k-3) = 3^A000045(k-1)*7^A000045(k-2) for k >=2.

%F a(2k+1) = a(2k)*a(2k-1) = 3^A000045(k+1)*7^A000045(k) for k>=1. (End)

%p f:= proc(n) if n::even then 3^combinat:-fibonacci(n/2-1)*7^combinat:-fibonacci(n/2-2)

%p else 3^combinat:-fibonacci((n+1)/2)*7^combinat:-fibonacci((n-1)/2)

%p fi

%p end proc:

%p map(f, [\$1..20]); # _Robert Israel_, Dec 05 2016

%t nxt[{a_,b_}]:={a*b,(a*b)/b}; NestList[nxt,{3,7},10]//Flatten (* _Harvey P. Dale_, Sep 06 2020 *)

%Y Cf. A000045, A115033, A115034, A115043.

%K nonn,easy

%O 1,1

%A _Giovanni Teofilatto_, Mar 16 2010

%E a(18) corrected by _Robert Israel_, Dec 05 2016

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Last modified July 24 15:05 EDT 2021. Contains 346273 sequences. (Running on oeis4.)