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

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A130913 Composite solutions to the equation phi(x)+sigma(x) = 2*reversal(x). 1
 44722206, 69067317, 460647525, 485700768, 427528099084 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS For a prime p we have phi(p)+sigma(p) = 2*reversal(p) iff p is a palindrome. a(6) > 10^12. - Giovanni Resta, Nov 03 2012 LINKS Table of n, a(n) for n=1..5. EXAMPLE 485700768 is in the sequence because 485700768 is composite and phi(485700768)+sigma(485700768) = 1734015168 = 2*867007584. MATHEMATICA Do[a=FromDigits[Reverse[IntegerDigits[n]]]; If[a>n&&EulerPhi[n]+ DivisorSigma[1, n]==2a, Print[n]], {n, 250000000}] (* Farideh Firoozbakht, Nov 26 2013 *) CROSSREFS Cf. A000010, A000203, A004086, A130000, A230020. Sequence in context: A172718 A270611 A049360 * A213353 A205263 A087534 Adjacent sequences: A130910 A130911 A130912 * A130914 A130915 A130916 KEYWORD hard,more,nonn,base AUTHOR Farideh Firoozbakht, Jun 09 2007 EXTENSIONS a(5) from Giovanni Resta, Nov 03 2012 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 18 11:13 EDT 2024. Contains 374378 sequences. (Running on oeis4.)