

A092645


Number of consecutive prime runs of just 4 primes congruent to 1 mod 4 below 10^n.


2



0, 0, 2, 10, 124, 1047, 8756, 78845, 703152, 6387276, 58448789
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OFFSET

1,3


COMMENTS

Conjecture: a(n) ~ 10^n / (64 log 10 * n).  Charles R Greathouse IV, Oct 24 2011


LINKS

Table of n, a(n) for n=1..11.


FORMULA

Generate the prime sequence with primes labeled 1 mod 4 or 3 mod 4. Add count of primes to sequence if just 4 primes occur before interruption by a prime congruent to 3 mod 4.


EXAMPLE

a(5)=124 because 124 sets of 4 primes occur below 10^5, each run interrupted by a prime congruent to 3 mod 4.


MATHEMATICA

p1 = p3 = 0; p = 15; s = Mod[{2, 3, 5, 7, 11, 13}, 4]; Do[ While[p < 10^n, If[s == {3, 1, 1, 1, 1, 3}, p1++]; If[s == {1, 3, 3, 3, 3, 1}, p3++]; p = NextPrime@ p; s = Join[ Take[s, 5], {Mod[p, 4]}]]; Print[{p1, p3}], {n, 2, 9}] (* Robert G. Wilson v, Sep 30 2011 *)


PROG

(PARI) a(n)=my(s, t); forprime(p=2, nextprime(10^n), if(p%4==1, t++, s+=t==4; t=0)); s \\ Charles R Greathouse IV, Oct 24 2011


CROSSREFS

Cf. A092646, A092647.
Sequence in context: A060690 A013038 A005321 * A202950 A144835 A119191
Adjacent sequences: A092642 A092643 A092644 * A092646 A092647 A092648


KEYWORD

more,nonn,changed


AUTHOR

Enoch Haga, Mar 02 2004


EXTENSIONS

a(11) from Chai Wah Wu, Mar 18 2018


STATUS

approved



