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 A106497 Numbers whose square is the concatenation of two identical numbers, i.e., of the form NN. 47
 36363636364, 45454545455, 54545454546, 63636363637, 72727272728, 81818181819, 90909090910, 428571428571428571429, 571428571428571428572, 714285714285714285715, 857142857142857142858 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS For the corresponding numbers N see A102567. Numbers of the form j*(10^d + 1)/k where 10^d + 1 == 0 (mod k^2) and k/sqrt(10) < j < k. - David W. Wilson, Nov 09 2006 REFERENCES R. Ondrejka, Problem 1130: Biperiod Squares, Journal of Recreational Mathematics, Vol. 14:4 (1981-82), 299. Solution by F. H. Kierstead, Jr., JRM, Vol. 15:4 (1982-83), 311-312. LINKS David W. Wilson, Table of n, a(n) for n = 1..1098 EXAMPLE 63636363637 is in the sequence because 63636363637^2 = 4049586776940495867769 is 40495867769 written twice. CROSSREFS Cf. A092118, A102567. Sequence in context: A022262 A233849 A116279 * A204097 A295355 A178221 Adjacent sequences:  A106494 A106495 A106496 * A106498 A106499 A106500 KEYWORD base,nonn AUTHOR Lekraj Beedassy, May 04 2005 EXTENSIONS a(7) from Klaus Brockhaus, May 06 2005 More terms from David W. Wilson, Nov 05 2006 Reference and cross-references added by William Rex Marshall, Nov 12 2010 STATUS approved

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Last modified October 14 01:36 EDT 2019. Contains 327994 sequences. (Running on oeis4.)