The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A135242 Numbers n such that sigma(n) = 2*(n-reversal(n)). 1
 10, 51, 430, 591, 922, 5991, 8350, 20210, 28810, 59211, 59991, 6673581, 8179030, 20158910, 203887910, 833549650, 2263048910, 2814442310, 7823347543, 78551146723, 81896108650, 281444442310, 770920338133, 832428872110, 7670112536751 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS If n=6*10^m-9 is semiprime then n is in the sequence (the proof is easy). a(26) > 10^13. - Giovanni Resta, Jul 13 2015 LINKS Table of n, a(n) for n=1..25. EXAMPLE sigma(51)=72=2*(51-15)=2*(51-reversal(51)), so 51 is in the sequence. MATHEMATICA Do[If[2(n-FromDigits@Reverse@IntegerDigits@n)==DivisorSigma[1, n], Print[n]], {n, 70000000}] CROSSREFS Cf. A000203, A004086, A135243. Sequence in context: A030183 A224327 A219573 * A362673 A041186 A058827 Adjacent sequences: A135239 A135240 A135241 * A135243 A135244 A135245 KEYWORD base,more,nonn AUTHOR Farideh Firoozbakht, Jan 04 2008 EXTENSIONS a(15)-a(21) from Donovan Johnson, Dec 21 2008 a(22)-a(25) from Giovanni Resta, Jul 13 2015 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified July 13 17:55 EDT 2024. Contains 374285 sequences. (Running on oeis4.)