A074814 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).

10, 25, 37, 40, 81, 102, 120, 204, 295, 340, 350, 387, 397, 1620, 1743, 2995, 3627, 3997, 4450, 4629, 4999, 8090, 8490, 9201, 9301, 10002, 12310, 17043, 20004, 22954, 29995, 30006, 36027, 39997, 40008, 40240, 42540, 42958, 46029, 49999, 55550, 60360, 65460, 82180, 85480, 200004

Offset

1,1

Links

Table of n, a(n) for n=1..46.

Example

10 is included since there are four primes between 10 and 1 and four primes between 10 and 20.

Prog

(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))}
{ for(n=1, 10^5, if(ok(n), print1(n, ", "))) } \\ Andrew Howroyd, Feb 12 2020

Crossrefs

Sequence in context: A014090 A345651 A154057 * A002600 A087473 A014120

Adjacent sequences: A074811 A074812 A074813 * A074815 A074816 A074817

Keyword

base,nonn

Author

Jason Earls, Sep 08 2002

Extensions

More terms from Sascha Kurz, Feb 10 2003

Terms a(28) and beyond from Andrew Howroyd, Feb 12 2020

Status

approved