%I #17 Sep 30 2019 10:13:23

%S 11,42,93,110,113,156,186,196,197,220,252,292,298,362,403,429,493,503,

%T 609,644,659,727,735,778,790,886,888,920,932,952,953,1008,1023,1024,

%U 1079,1093,1094,1100,1109,1136,1165,1208,1212,1213,1226,1238,1250,1311

%N Numbers that occur exactly once in A289493 (= number of primes between 2n and 3n).

%t f[n_] := PrimePi[3n] - PrimePi[2n]; t = Split[ Sort[ Table[ f[n], {n, 14000}] ]]; Flatten[ Select[t, Length[ # ] == 1 &]] (* _Robert G. Wilson v_, Feb 10 2005 *)

%o (PARI) bet2n3n(n)={ my(b=vecsort( vector(n,x, my(c=0); forprime(y=2*x+1,3*x-1, c++); c))); for(x=1,n-2, if(b[x+1]>b[x] && b[x+1]<b[x+2], print1(b[x+1]",")))} \\ Probably using A289493 and/or primepi(3n)-primepi(2n) would be faster. Edited and corrected by _M. F. Hasler_, Sep 29 2019

%o (PARI) \\ Size of vector dependent on how pessimistic one is on smoothness of primepi

%o primecount(a, b)=primepi(b)-primepi(a);

%o v=vector(14000);

%o for(k=1, oo, j=primecount(2*k, 3*k); if(j>#v, break, v[j]++));

%o for(k=1, 1311, if(v[k]==1, print1(k, ", "))) \\ _Hugo Pfoertner_, Sep 29 2019

%Y Cf. A289493, A101984.

%K easy,nonn

%O 1,1

%A _Cino Hilliard_, Jan 29 2005

%E More terms from _Robert G. Wilson v_, Feb 10 2005

%E Name edited by _M. F. Hasler_, Sep 29 2019