OFFSET
1,3
FORMULA
Generate the odd nonprime sequence with nonprimes labeled 1 mod 4 or 3 mod 4. Add count of nonprimes to sequence if 3 nonprimes congruent to 3 mod 4 occur before interruption of a nonprime congruent to 1 mod 4
EXAMPLE
a(3)=5 because 5 nonprime runs of 3 occur below 10^3, each run interrupted by a nonprime congruent to 1 mod 4.
MATHEMATICA
A091113 = Select[4 Range[0, 10^4] + 1, ! PrimeQ[#] &];
A091236 = Select[4 Range[0, 10^4] + 3, ! PrimeQ[#] &];
lst = {}; Do[If[Length[s = Select[A091236, Between[{A091113[[i]], A091113[[i + 1]]}]]] == 3, AppendTo[lst, Last[s]]], {i, Length[A091113] - 1}]; Table[Count[lst, x_ /; x < 10^n], {n, 4}] (* Robert Price, May 31 2019 *)
CROSSREFS
KEYWORD
more,nonn
AUTHOR
Enoch Haga, Mar 30 2004
EXTENSIONS
a(9)-a(13) from Bert Dobbelaere, Dec 19 2018
STATUS
approved