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, 2, 2, 4, 8, 32, 24, 64, 144, 64, 864, 512, 4320, 2048, 8640, 16384, 8640, 131072, 8640, 1048576, 8640, 8388608, 69120, 50331648, 345600, 150994944, 345600, 452984832, 1382400, 452984832, 5529600, 2264924160, 11059200, 2264924160, 22118400, 4529848320, 88473600, 36238786560, 265420800

Offset

1,2

Comments

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

Links

Jean-Marc Falcoz, Table of n, a(n) for n = 1..202

Example

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.

Maple

a:= proc(n) option remember; `if`(n<3, n,
      a(n-2)*iquo(a(n-1), 10^(length(a(n-1))-1)))
    end:
seq(a(n), n=1..50);  # Alois P. Heinz, Mar 12 2018

Mathematica

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

Prog

(PARI) a(n) = if(n==1, 1, if(n==2, 2, a(n-2)*digits(a(n-1))[1])) \\ Felix Fröhlich, Mar 12 2018

Crossrefs

Cf. A000079.

Sequence in context: A145869 A032439 A096096 * A100799 A070323 A109213

Adjacent sequences: A300756 A300757 A300758 * A300760 A300761 A300762

Keyword

nonn,base

Author

Eric Angelini and Jean-Marc Falcoz, Mar 12 2018

Status

approved