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%I #14 Jul 01 2022 10:10:53
%S 1,2,21,122,22112,21122221,1222211221122,221122112222112222112,
%T 2112222112222112211222211221122221,
%U 1222211221122221122112222112222112211222211222211221122
%N a(1) = 1, a(2) = 2, a(n) = reverse concatenation of two previous terms.
%C Concatenation of any three successive terms is a palindrome.
%C a(17) with 1597 digits is the first term > 10^1000. - _Michael S. Branicky_, Jul 01 2022
%H Michael S. Branicky, <a href="/A091789/b091789.txt">Table of n, a(n) for n = 1..16</a>
%p Rcat := proc(a,b) local resul,digs ; digs := convert(b,base,10) ; resul := 0 ; for k in digs do resul := resul*10+k ; od ; digs := convert(a,base,10) ; for k in digs do resul := resul*10+k ; od ; RETURN(resul) ; end: A091789 := proc(nmax) local a,anxt,n,i,j; a := [1,2] ; for n from 3 to nmax do a := [op(a),Rcat(op(-2,a),op(-1,a))] ; od; RETURN(a) ; end: op(A091789(13)) ; # _R. J. Mathar_, Jul 26 2007
%o (Python)
%o from itertools import count, islice
%o def agen():
%o s, t = "1", "2"
%o yield from [1, 2]
%o while True:
%o s, t = t, (s+t)[::-1]
%o yield int(t)
%o print(list(islice(agen(), 11))) # _Michael S. Branicky_, Jul 01 2022
%Y Cf. A091790.
%K base,nonn
%O 1,2
%A _Amarnath Murthy_, Feb 18 2004
%E More terms from _R. J. Mathar_, Jul 26 2007
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