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 A110076 a(n) is the largest number m such that sigma(m)=10^n, or if there is no such m a(n)=0. 4
 1, 0, 0, 0, 9481, 99301, 997501, 9993001, 99948001, 999795001, 9999750001, 99998670001, 999997950001, 9999986700001, 99999975000001, 999999198750001, 9999999187500001, 99999995096707501, 999999919987500001, 9999999986700000001, 99999499999999800001, 999999999907500000001, 9999999999796009687501 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,5 COMMENTS Conjecture: For n>3 a(n) is positive. For 4 <= n <= 102, a(n) is the product of two distinct primes, but a(103) = a(49)*a(54) and is the product of four distinct primes: 1862645149230957031249999 * 5368709119999999999999999 * 79999999999999999999999999 * 12499999999999999999999999999. - David Wasserman, Nov 18 2008 LINKS Max Alekseyev, Table of n, a(n) for n = 0..1000 Max A. Alekseyev, Computing the Inverses, their Power Sums, and Extrema for Euler's Totient and Other Multiplicative Functions. Journal of Integer Sequences, Vol. 19 (2016), Article 16.5.2 EXAMPLE a(12)=999997950001 because sigma(999997950001)=sigma(799999*1249999) =800000*1250000=10^12 and 999997950001 is the largest number with this property(sigma(m)=10^12). MATHEMATICA a = 1; a = a = a = 0; a[n_] := (For[m = 1, DivisorSigma[ 1, 10^n - m] != 10^n, m++ ]; 10^n - m); Do[Print[a[n]], {n, 0, 12}] CROSSREFS Cf. A110077, A110078. Sequence in context: A235734 A235515 A161726 * A204722 A204961 A237104 Adjacent sequences: A110073 A110074 A110075 * A110077 A110078 A110079 KEYWORD nonn AUTHOR Farideh Firoozbakht, Jul 31 2005 EXTENSIONS More terms from David Wasserman, Nov 18 2008 Terms a(19) onward from Max Alekseyev, Mar 06 2014 STATUS approved

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Last modified February 1 08:20 EST 2023. Contains 359992 sequences. (Running on oeis4.)