A160265 Each of the numbers describes the previous number, and is described by the next number.

1, 11, 12, 1121, 1321, 123121, 132231, 123222, 112431, 13214131, 14322141, 13423122, 12324123, 12233241, 12233241, 12233241, 12233241, 12233241, 12233241, 12233241, 12233241, 12233241, 12233241, 12233241, 12233241, 12233241, 12233241, 12233241, 12233241, 12233241

Offset

1,2

Comments

Starting with 1, each of the rest describes the previous number in a "digit + number_of_digits" manner. The odd-indexed digits are digits that appeared in the previous term, ordered by the first appearance. The even-indexed digits are how many times that digit appeared. [Edited by Michel Marcus, Oct 26 2021]

Links

Table of n, a(n) for n=1..30.

Mathematica

NestList[FromDigits@Flatten@Tally@IntegerDigits@#&, 1, 30] (* Giorgos Kalogeropoulos, Oct 26 2021 *)

Prog

(PARI) lista(nn) = {my(v = vector(nn)); v[1] = 1; for (n=2, nn, my(vd = digits(v[n-1]), vu = Set(vd), vw = vector(#vu), pos=0, ss=""); for (i=1, #vd, if (!setsearch(Set(vw), vd[i]), pos++; vw[pos] = vd[i]); ); for (i=1, #vw, ss = concat(ss, vw[i]); ss = concat(ss, #select(x->(x==vw[i]), vd)); ); v[n] = eval(ss); ); v; } \\ Michel Marcus, Oct 26 2021

Crossrefs

A variant of A005150. See Index entries under "Say what you see". - N. J. A. Sloane, May 10 2009

Cf. A121808.

Sequence in context: A087304 A340204 A121808 * A007651 A022481 A156338

Adjacent sequences: A160262 A160263 A160264 * A160266 A160267 A160268

Keyword

nonn,base

Author

Adrian Lee (prof.adrian.lee(AT)gmail.com), May 07 2009

Extensions

More terms from Michel Marcus, Oct 26 2021

Status

approved