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 A030512 Concatenation of first n 2-digit positive integers including leading zeros. 3
 1, 102, 10203, 1020304, 102030405, 10203040506, 1020304050607, 102030405060708, 10203040506070809, 1020304050607080910, 102030405060708091011, 10203040506070809101112, 1020304050607080910111213, 102030405060708091011121314 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS From Peter Bala, Sep 14 2015: (Start) Empirically, we observe that the square roots of these numbers and their reciprocals have some interesting properties, as follows (examples are given below). The decimal expansion of sqrt(a(n)) begins with strings of repeated digits (that gradually shorten in length until they disappear) alternating with strings of apparently random digits. The decimal expansion of 1/sqrt(a(n)) has long strings of 0's (gradually shortening in length until they disappear) interspersed with blocks of digits. If we read these blocks of digits as ordinary integers and factorize them, we find the numbers are related in a surprising manner. Cf. A014824. (End) LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..200 FORMULA a(n+1) = 100*a(n) + n + 1 for n<100. a(n+1) = -(199/9801) - (1/99)*n + (10000/9801)*100^n, with n >= 1. - Paolo P. Lava, Oct 09 2008 EXAMPLE From Peter Bala, Sep 14 2015: (Start) Decimal expansions with repeating strings of digits in parentheses for clarity: sqrt(a(50)) = 1.(0101...0101)0075(5050...5050)4728503 (7878...7878)7065734690(6565...6565)63090366531526199 (4949...4949)40423435587935014204(5454...5454) 511096186531728108723958(33...33)197004273464583079020182291 (66...66)107291492892700779438018798828124(99...99) 7645962810367893557912773556179470486(11...11) 010064064746152... * 10^49. 1/sqrt(a(10))  = 9.9(0...0)53955(0...0)441082125(0..0)4... * 10^(-10). The long strings of zeros gradually shorten in length until they disappear and are interspersed with five blocks of digits [99, 53955, 441082125, 400649596875, 38211955301953125] = [3^2*11, 3^2*5*11*109, 3^3*5^3*11*109^2, 3^2*5^5*11*109^3, 3^2*5^8*7*11*109^4]. (End) MATHEMATICA Table[-(199/9801)-(1/99) n + (10000/9801) 100^n, {n, 0, 20}] (* Vincenzo Librandi, May 17 2013 *) PROG (MAGMA) [-(199/9801)-(1/99)*n+(10000/9801)*100^n: n in [0..20]]; // Vincenzo Librandi, May 17 2013 (PARI) a(n) = -(199/9801) - (1/99)*(n-1) + (10000/9801)*100^(n-1); vector(30, n, a(n)) \\ Altug Alkan, Oct 01 2015 CROSSREFS Cf. A014824. Sequence in context: A284448 A274252 A303993 * A097725 A129751 A225993 Adjacent sequences:  A030509 A030510 A030511 * A030513 A030514 A030515 KEYWORD nonn,fini,base AUTHOR EXTENSIONS Edited by Charles R Greathouse IV, Apr 28 2010 STATUS approved

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Last modified March 20 15:43 EDT 2019. Contains 321345 sequences. (Running on oeis4.)