This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A069217 #10 Feb 11 2014 19:05:28 %S A069217 1,2,3,5,7,11,101,131,151,181,191,313,353,373,383,727,757,787,797,919, %T A069217 929,10301,10501,10601,11311,11411,12421,12721,12821,13331,13831, %U A069217 13931,14341,14741,15451,15551,16061,16361,16561,16661,17471,17971,18181 %N A069217 Numbers n such that phi(n) + sigma(n) = n + reversal(n). %C A069217 Note that all terms so far are palindromes. %C A069217 It is obvious that if n is a term of the sequence greater than 1 then n is prime iff n is a palindrome. Do there exist composite terms in the sequence? - _Farideh Firoozbakht_, Jan 28 2006 Answer: Yes, see next comment. %C A069217 Giovanni Resta writes (Sep 06 2006): The smallest composite number such that n+rev(n)=phi(n)+sigma(n) is n = 3197267223 = 3 * 79 * 677 * 19927 with rev(n) = 3227627913, phi(n) = 2101316256, sigma(n) = 4323578880 and 3197267223+3227627913 = 6424895136 = 2101316256+4323578880. %H A069217 Vincenzo Librandi, <a href="/A069217/b069217.txt">Table of n, a(n) for n = 1..700</a> %F A069217 If p is prime and rev(p)=p then p+rev(p)=2p=phi(p)+sigma(p) so all palindromic primes are in the sequence. - _Farideh Firoozbakht_, Sep 12 2006 %e A069217 phi(101) + sigma(101) = 202 = 101 + 101 = 101 + reversal(101). %t A069217 Select[Range[5*10^4], EulerPhi[ # ] + DivisorSigma[1, # ] == # + FromDigits[Reverse[IntegerDigits[ # ]]] &] %Y A069217 Contains composite terms, so is strictly different from A002385. %K A069217 base,nonn %O A069217 1,2 %A A069217 _Joseph L. Pe_, Apr 11 2002