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 A230020 Composite numbers n such that sigma(n) - reversal(n) = 1. 2
 9599, 31874, 93689, 932639, 1367991, 13451831, 309173753, 99148830299 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS It is obvious that palindromic primes (palprimes) are all prime solutions of the equation sigma(x)-reversal(x) = 1. The next term is greater than 73*10^7. a(9) > 10^12. - Giovanni Resta, Dec 14 2013 LINKS Table of n, a(n) for n=1..8. EXAMPLE sigma(9599) = sigma(29*331) = 30*332 = 9960 = reverse(9599)+1. MATHEMATICA Do[a=FromDigits[Reverse[IntegerDigits[n]]]; If[a>n && DivisorSigma[1, n] -a == 1, Print[n]], {n, 730000000}] CROSSREFS Cf. A000203, A002385, A004086, A130000. Sequence in context: A250761 A038825 A038814 * A034626 A031596 A236715 Adjacent sequences: A230017 A230018 A230019 * A230021 A230022 A230023 KEYWORD nonn,base,more AUTHOR Farideh Firoozbakht, Nov 26 2013 EXTENSIONS a(8) from Giovanni Resta, Dec 14 2013 STATUS approved

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Last modified May 20 19:00 EDT 2024. Contains 372720 sequences. (Running on oeis4.)