A092645 - OEIS

The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

A092645

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

0, 0, 2, 10, 124, 1047, 8756, 78845, 703152, 6387276, 58448789 (list; graph; refs; listen; history; text; internal format)

	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 A305028` `Adjacent sequences: A092642 A092643 A092644 * A092646 A092647 A092648`
	KEYWORD	`more,nonn`
	AUTHOR	`Enoch Haga, Mar 02 2004`
	EXTENSIONS	`a(11) from Chai Wah Wu, Mar 18 2018`
	STATUS	`approved`

Last modified February 23 00:56 EST 2020. Contains 332157 sequences. (Running on oeis4.)