cp's OEIS Frontend

A101983 Numbers that do not occur in A101909 (= number of primes between 2n and 4n).

%I A101983 #13 Oct 02 2019 01:56:18
%S A101983 11,79,134,184,186,215,245,262,284,305,387,544,694,700,706,776,814,
%T A101983 881,939,974,1002,1027,1079,1104,1133,1146,1184,1193,1207,1354,1387,
%U A101983 1415,1441,1495,1574,1587,1608,1662,1690,1801,1915,1987,2054,2067,2104,2170
%N A101983 Numbers that do not occur in A101909 (= number of primes between 2n and 4n).
%e A101983 11 is the first number that does not equal a count of primes between 2n and 4n for some n.
%t A101983 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 *)
%o A101983 (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
%o A101983 (PARI) primecount(a,b)=primepi(b)-primepi(a);
%o A101983 v=vector(20000);
%o A101983 for(k=1,oo,j=primecount(2*k,4*k);if(j>#v,break,v[j]++));
%o A101983 for(k=1,2170,if(v[k]==0,print1(k,", "))) \\ _Hugo Pfoertner_, Sep 29 2019
%Y A101983 Complement of A101947.
%Y A101983 Cf. A101909.
%K A101983 easy,nonn
%O A101983 1,1
%A A101983 _Cino Hilliard_, Jan 28 2005
%E A101983 More terms from _Robert G. Wilson v_, Feb 10 2005
%E A101983 Name edited by _M. F. Hasler_, Sep 29 2019