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 A038395 Concatenate the first n odd numbers in reverse order. 4

%I

%S 1,31,531,7531,97531,1197531,131197531,15131197531,1715131197531,

%T 191715131197531,21191715131197531,2321191715131197531,

%U 252321191715131197531,27252321191715131197531

%N Concatenate the first n odd numbers in reverse order.

%C a(n) starts with the digits of 2n-1. Indices of prime or probable prime terms are 1,2,37,62,409,...: see also A089922. - _M. F. Hasler_, Apr 13 2008

%C If n == 0 (mod 3), so is a(n). - _Sergey Pavlov_, Mar 29 2017

%D Mihaly Bencze [Beneze] and L. Tutescu, Some Notions and Questions in Number Theory, Sequence 3.

%H Florentin Smarandache, <a href="http://arXiv.org/abs/math/0604019">Sequences of Numbers Involved in Unsolved Problems</a>, arXiv:math/0604019 [math.GM], 2006.

%F a(n) = (2*n-1)*10^floor{1+log10[a(n-1)]}+a(n-1), with a(1)=1. - _Paolo P. Lava_, Jun 19 2008

%p P:=proc(i) local a,n; a:=1; print(a); for n from 2 by 1 to i do a:=(2*n-1)*10^floor(evalf(1+log10(a),100))+a ; print(a); od; end: P(100); # _Paolo P. Lava_, Jun 19 2008

%t Table[FromDigits[Flatten[IntegerDigits/@Join[Reverse[Range[1,n,2]]]]], {n,1,29,2}] (* _Harvey P. Dale_, Jun 02 2011 *)

%o (PARI) t=""; for( n=1,10^3, ( t=eval( Str( 2*n-1,t))) & print(n" "t)) \\ _M. F. Hasler_, Apr 13 2008

%Y Cf. A089922, A109837, A038394-A038399, A019518, A019519.

%K nonn,base,easy

%O 1,2

%A M. I. Petrescu (mipetrescu(AT)yahoo.com)

%E Edited and extended by _M. F. Hasler_, Apr 13 2008

%E Edited by _T. D. Noe_, Oct 30 2008

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Last modified October 19 04:40 EDT 2019. Contains 328211 sequences. (Running on oeis4.)