A259747 a(0) = 1; thereafter a(n) is the concatenation of a(n-1), n, a(n-1).

1, 111, 1112111, 111211131112111, 1112111311121114111211131112111, 111211131112111411121113111211151112111311121114111211131112111

Offset: 0

Author

José María Grau Ribas, Jul 04 2015

Keywords

• nonn
• base

Crossrefs

Cf. A001704, A007908.

Programs

Mathematica

concatPal[0] = 1; concatPal[n_] := FromDigits @ Join[RealDigits[concatPal[n - 1]][[1]], {n}, RealDigits[concatPal[n - 1]][[1]]]; Table[concatPal[n], {n, 0, 10}]
nxt[{n_,a_}]:={n+1,FromDigits[Flatten[Join[IntegerDigits[a], IntegerDigits[ n+1], IntegerDigits[ a]]]]}; NestList[nxt,{0,1},5][[All,2]] (* Harvey P. Dale, Apr 30 2020 *)

PARI

main(size) = {s=vector(size); s[1]=1; for(t=2,size,s[t]= eval(Str(s[t-1],t-1,s[t-1]))); return(s);} \\ Anders Hellström, Jul 05 2015

Formula

a(1)=1 and a(n) = a(n - 1)*10^(2^n) + n *10^(2^n - 1) + a(n - 1).