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 A135243 Numbers n such that sigma(n) = 6*(reversal(n)-n). 1
 34, 394, 3994, 39994, 2309882, 3070463, 7796129, 205207782, 225073882, 478854106, 644154038, 1556396391, 3154222593, 3165974493, 5951924107, 10444787521, 12114130241, 20611191282, 58403366517, 71103822309 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS If n=4*10^m-6 is a semiprime (and 2*10^m-3 is prime) then n is in the sequence (the proof is easy). Next term is greater than 7*10^7. LINKS Table of n, a(n) for n=1..20. EXAMPLE sigma(34)=54=6*(43-34)=6*(reversal(34)-34), so 34 is in the sequence. MATHEMATICA Do[If[6(FromDigits@Reverse@IntegerDigits@n-n)==DivisorSigma[1, n], Print[n]], {n, 70000000}] CROSSREFS Cf. A000203, A004086, A135242. Sequence in context: A168122 A271756 A228995 * A283227 A033914 A189452 Adjacent sequences: A135240 A135241 A135242 * A135244 A135245 A135246 KEYWORD base,nonn AUTHOR Farideh Firoozbakht, Jan 04 2008 EXTENSIONS a(8)-a(20) from Donovan Johnson, Dec 21 2008 STATUS approved

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Last modified August 15 01:22 EDT 2024. Contains 375171 sequences. (Running on oeis4.)