A101983 - OEIS

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A101983

Numbers that do not occur in A101909 (= number of primes between 2n and 4n).

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