Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #11 Feb 12 2020 19:05:51
%S 10,25,37,40,81,102,120,204,295,340,350,387,397,1620,1743,2995,3627,
%T 3997,4450,4629,4999,8090,8490,9201,9301,10002,12310,17043,20004,
%U 22954,29995,30006,36027,39997,40008,40240,42540,42958,46029,49999,55550,60360,65460,82180,85480,200004
%N Numbers k such that the number of primes between k and 2k (inclusive) is equal to the number of primes between k and reverse(k) (inclusive).
%e 10 is included since there are four primes between 10 and 1 and four primes between 10 and 20.
%o (PARI) ok(n)={my(r=fromdigits(Vecrev(digits(n)))); if(r>n, primepi(2*n) == primepi(r), primepi(n) - primepi(r-1) == primepi(2*n) - primepi(n-1))}
%o { for(n=1, 10^5, if(ok(n), print1(n, ", "))) } \\ _Andrew Howroyd_, Feb 12 2020
%K base,nonn
%O 1,1
%A _Jason Earls_, Sep 08 2002
%E More terms from _Sascha Kurz_, Feb 10 2003
%E Terms a(28) and beyond from _Andrew Howroyd_, Feb 12 2020