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A101985
Numbers that occur exactly once in A289493 (= number of primes between 2n and 3n).
4
11, 42, 93, 110, 113, 156, 186, 196, 197, 220, 252, 292, 298, 362, 403, 429, 493, 503, 609, 644, 659, 727, 735, 778, 790, 886, 888, 920, 932, 952, 953, 1008, 1023, 1024, 1079, 1093, 1094, 1100, 1109, 1136, 1165, 1208, 1212, 1213, 1226, 1238, 1250, 1311
OFFSET
1,1
MATHEMATICA
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 *)
PROG
(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
(PARI) \\ Size of vector dependent on how pessimistic one is on smoothness of primepi
primecount(a, b)=primepi(b)-primepi(a);
v=vector(14000);
for(k=1, oo, j=primecount(2*k, 3*k); if(j>#v, break, v[j]++));
for(k=1, 1311, if(v[k]==1, print1(k, ", "))) \\ Hugo Pfoertner, Sep 29 2019
CROSSREFS
Sequence in context: A003356 A063152 A338627 * A055437 A055436 A213772
KEYWORD
easy,nonn
AUTHOR
Cino Hilliard, Jan 29 2005
EXTENSIONS
More terms from Robert G. Wilson v, Feb 10 2005
Name edited by M. F. Hasler, Sep 29 2019
STATUS
approved