A066547 - OEIS

%I #9 May 09 2014 06:12:15

%S 1,23,456,7891,1112,131415,1617181,92021222,324252627,2829303132,

%T 33343536373,839404142434,4454647484950,51525354555657,

%U 585960616263646,5666768697071727,37475767778798081,828384858687888990,9192939495969798991,101102103104105106,107108109110111112113

%N Let N = 123456789101112131415161718..., the concatenation of the natural numbers. a(n) is the n-digit number formed from the digits of N starting from the {n(n-1)/2 +1}th digit. Omit any leading zeros.

%H Vincenzo Librandi, <a href="/A066547/b066547.txt">Table of n, a(n) for n = 1..71</a>

%e 1, 23, 456, 7891, 01112, 131415, 1617181, 92021222, 3... becomes 1, 23, 456, 7891, 1112, 131415, 1617181, 92021222, ...

%t d = Flatten[IntegerDigits /@ Range[90]]; Table[FromDigits[Take[d, {n(n + 1)/2 + 1, (n + 1)(n + 2)/2}]], {n, 0, 17}] (* _Robert G. Wilson v_, Nov 22 2004 *)

%o (PARI) N=[]; k=0; for(n=1,20, while(#N<n, N=concat(N,Vec(Str(k++)))); print1(eval(concat(vecextract(N,2^n-1)))","); N=vecextract(N,Str("^.."n))) \\ _M. F. Hasler_, May 08 2014

%Y Cf. A100751, A007376, A033307, A066548.

%Y Cf. A001369, A007923.

%K nonn,base

%O 1,2

%A _Amarnath Murthy_, Dec 16 2001

%E More terms from Larry Reeves (larryr(AT)acm.org), Dec 18 2001