A110401 a(1) = 999, a(n) is the number obtained by concatenating product of neighboring digits of the previous term.

999, 8181, 888, 6464, 242424, 88888, 64646464, 24242424242424, 8888888888888, 646464646464646464646464, 2424242424242424242424242424242424242424242424, 888888888888888888888888888888888888888888888

Offset

1,1

Comments

If one uses any other number as a(1), the sequence either comes to an end with a single-digit term or eventually contains increasing strings of 8, 64 and 24 repeatedly. E.g., a(1) = 1234 gives 1234, 2612, 1262, 21212, 2222, 444, 1616, 666, 3636, 181818, 88888, 64646464, 24242424242424, 8888888888888, ...

Links

Table of n, a(n) for n=1..12.

Prog

(PARI) f(n) = my(d=digits(n), nd=[]); for (k=1, #d-1, nd = concat(nd, digits(d[k]*d[k+1]))); fromdigits(nd);
a(n) = if (n==1, 999, f(a(n-1))); \\ Michel Marcus, Dec 08 2018

Crossrefs

Sequence in context: A226752 A043527 A117720 * A213156 A164813 A164814

Adjacent sequences: A110398 A110399 A110400 * A110402 A110403 A110404

Keyword

base,easy,nonn

Author

Amarnath Murthy, Jul 29 2005

Extensions

Corrected and extended by Joshua Zucker, May 10 2006

Edited by Jon E. Schoenfield, Dec 08 2018

Status

approved