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 A101983 Numbers that do not occur in A101909 (= number of primes between 2n and 4n). 3
 11, 79, 134, 184, 186, 215, 245, 262, 284, 305, 387, 544, 694, 700, 706, 776, 814, 881, 939, 974, 1002, 1027, 1079, 1104, 1133, 1146, 1184, 1193, 1207, 1354, 1387, 1415, 1441, 1495, 1574, 1587, 1608, 1662, 1690, 1801, 1915, 1987, 2054, 2067, 2104, 2170 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Table of n, a(n) for n=1..46. EXAMPLE 11 is the first number that does not equal a count of primes between 2n and 4n for some n. MATHEMATICA f[n_] := PrimePi[4n] - PrimePi[2n]; t = Union[ Table[ f[n], {n, 12000}]]; Complement[ Range[ t[[ -1]]], t] (* Robert G. Wilson v, Feb 10 2005 *) PROG (PARI) bet2n4n(n)={ my( b=vecsort(vector(n, x, my(c=0); forprime(y=2*x+1, 4*x-1, c++); c))); for(x=1, n-2, while(b[x+1]-b[x]>1, print1(b[x]++, ", ")))} \\ It's probably faster to use A101909 instead of forprime(...). Edited and corrected by M. F. Hasler, Sep 29 2019 (PARI) primecount(a, b)=primepi(b)-primepi(a); v=vector(20000); for(k=1, oo, j=primecount(2*k, 4*k); if(j>#v, break, v[j]++)); for(k=1, 2170, if(v[k]==0, print1(k, ", "))) \\ Hugo Pfoertner, Sep 29 2019 CROSSREFS Complement of A101947. Cf. A101909. Sequence in context: A225896 A239437 A140542 * A139953 A111067 A172067 Adjacent sequences: A101980 A101981 A101982 * A101984 A101985 A101986 KEYWORD easy,nonn AUTHOR Cino Hilliard, Jan 28 2005 EXTENSIONS More terms from Robert G. Wilson v, Feb 10 2005 Name edited by M. F. Hasler, Sep 29 2019 STATUS approved

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Last modified September 11 05:21 EDT 2024. Contains 375814 sequences. (Running on oeis4.)