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%I #14 May 30 2021 15:28:56
%S 1,13,139,13927,1392781,1392781243,1392781243729,13927812437292187,
%T 139278124372921876561,13927812437292187656119683,
%U 1392781243729218765611968359049,1392781243729218765611968359049177147,1392781243729218765611968359049177147531441
%N Concatenation of 3^k, k = 0,..,n.
%D A. Murthy, Smarandache Notions Journal, Vol. 11 N. 1-2-3 Spring 2000
%e 139 belongs to the sequence because it is the concatenation of 3^0, 3^1 and 3^2.
%p From _R. J. Mathar_, Oct 10 2010: (Start)
%p cat2 := proc(a,b) dgsb := max(1,ilog10(b)+1) ; a*10^dgsb+b ; end proc:
%p catL := proc(L) local a; a := op(1,L) ; for i from 2 to nops(L) do a := cat2(a,op(i,L)) ; end do; a; end proc:
%p A051639 := proc(n) catL([seq(3^k,k=0..n)]) ; end proc: seq(A051639(n),n=0..20) ; (End)
%p # second Maple program:
%p a:= proc(n) a(n):= `if`(n<0, 0, parse(cat(a(n-1), 3^n))) end:
%p seq(a(n), n=0..12); # _Alois P. Heinz_, May 30 2021
%t With[{p3=3^Range[0,15]},Table[FromDigits[Flatten[IntegerDigits/@ Take[ p3,n]]],{n,15}]] (* _Harvey P. Dale_, Sep 13 2011 *)
%Y Cf. A000244. - _R. J. Mathar_, Oct 10 2010
%K base,nonn
%O 0,2
%A _Felice Russo_, Nov 15 1999
%E Terms n>=7 corrected by _R. J. Mathar_, Oct 10 2010
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