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 A116163 Numbers k such that k concatenated with k+1 gives the product of two numbers which differ by 1. 8
 1, 5, 61, 65479, 84289, 106609, 225649, 275599, 453589, 1869505, 2272555, 2738291, 3221951, 1667833021, 2475062749, 2525062249, 3500010739, 9032526511, 9225507211, 1753016898055, 1860598847399, 3233666953849, 3379207972471, 5632076031055, 5823639407489 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Also numbers k such that k concatenated with k-1 gives the product of two numbers which differ by 3. LINKS Giovanni Resta, Table of n, a(n) for n = 1..2000 EXAMPLE 1 is a member since 12 = 3*4; also 10 = 2*5. 5 is a member since 56 = 7*8; also 54 = 6*9. MATHEMATICA Union @@ ((y /. List@ ToRules@ Reduce[x (x+1) == 10^# y +y+1 && x>0 && 10^(#-1) <= y+1 < 10^#, {x, y}, Integers]) & /@ Range[13] /. y->{}) (* Giovanni Resta, Jul 08 2018 *) CROSSREFS Cf. A116154, A115426, A116170, A116294. Cf. A116143, A102567, A116112, A116130, A116280. Sequence in context: A258672 A326571 A201254 * A092823 A152031 A302181 Adjacent sequences:  A116160 A116161 A116162 * A116164 A116165 A116166 KEYWORD nonn,base AUTHOR Giovanni Resta, Feb 06 2006 EXTENSIONS Edited by N. J. A. Sloane, Apr 15 2007, Jun 27 2009 More terms from Giovanni Resta, Jul 08 2018 STATUS approved

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Last modified March 29 18:26 EDT 2020. Contains 333116 sequences. (Running on oeis4.)