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A300759 Multiply a(n) by the first digit of a(n+1) to get a(n+2). The sequence starts with a(1) = 1 and a(2) = 2. 1

%I

%S 1,2,2,4,8,32,24,64,144,64,864,512,4320,2048,8640,16384,8640,131072,

%T 8640,1048576,8640,8388608,69120,50331648,345600,150994944,345600,

%U 452984832,1382400,452984832,5529600,2264924160,11059200,2264924160,22118400,4529848320,88473600,36238786560,265420800

%N Multiply a(n) by the first digit of a(n+1) to get a(n+2). The sequence starts with a(1) = 1 and a(2) = 2.

%C This sequence does not enter into a loop. The 200th term has 49 digits.

%H Jean-Marc Falcoz, <a href="/A300759/b300759.txt">Table of n, a(n) for n = 1..202</a>

%e 1*2 is 2; then 2*2 is 4; 2*4 is 8; 4*8 is 32; 8*3 = 24 (as 3 is the first digit of 32); 32*2 = 64 (as 2 is the first digit of 24); etc.

%p a:= proc(n) option remember; `if`(n<3, n,

%p a(n-2)*iquo(a(n-1), 10^(length(a(n-1))-1)))

%p end:

%p seq(a(n), n=1..50); # _Alois P. Heinz_, Mar 12 2018

%t nxt[{a_,b_}]:={b,a IntegerDigits[b][[1]]}; NestList[nxt,{1,2},40][[All,1]] (* _Harvey P. Dale_, Oct 04 2019 *)

%o (PARI) a(n) = if(n==1, 1, if(n==2, 2, a(n-2)*digits(a(n-1))[1])) \\ _Felix Fröhlich_, Mar 12 2018

%Y Cf. A000079.

%K nonn,base

%O 1,2

%A _Eric Angelini_ and _Jean-Marc Falcoz_, Mar 12 2018

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Last modified September 30 05:03 EDT 2020. Contains 337435 sequences. (Running on oeis4.)