A350827 Number of prime septuplets (i.e.: 7-tuples) with initial member (A022009 or A022010) between 10^(n-1) and 10^n.

0, 1, 0, 1, 1, 4, 5, 21, 70, 370, 1862, 9634

Offset

1,6

Comments

"Between 10^(n-1) and 10^n" is equivalent to saying "with n digits".

Up to 10^600 at least, the largest term of all prime septuplets (= set of 7 consecutive primes {p1, ..., p7} with minimal possible diameter p7 - p1 = 20) has the same number of digits as the smallest term. (*)

Terms a(1)-a(12) computed from b-files a(1..10^4) for A022009 and A022010.

(*) We checked that n = 1, 2, 3, 5, 17 and 18 are the only values below 600 with more than 2 primes in the interval [10^n - 20, 10^n + 20]. So the probability of finding a 7-tuple with diameter 20 in such an interval seems exceedingly small. - M. F. Hasler, Apr 12 2022

Links

Table of n, a(n) for n=1..12.

Example

a(1) = a(3) = 0 because there is no single-digit nor a 3-digit prime to start a prime septuplet.
a(2) = a(4) = a(5) = 1 because 11 = A022009(1), 5639 = A022010(1) and 88799 = A022010(2) are the only prime with 2, 4 resp. 5 digits to start a prime septuplet.
Then there are a(6) = 4 six-digit primes, 165701, 284729, 626609 and 855719, which start a prime septuplet.

Prog

(PARI) apply( {A350827(n, v=vector(6), c)=forprime(p=10^(n-1), 10^n, v[n=1+n%#v]+20==(v[n]=p) && c++); c}, [1..8]) \\ becomes slow for n > 8. - M. F. Hasler, Apr 12 2022

Crossrefs

Cf. A022009, A022010: initial members p of prime septuplets (p, p+2, p+6, ...) resp. (p, p+2, p+8, ...).

Cf. A350825, A350826, A350828: similar for quintuplets, sextuplets and octuplets.

Sequence in context: A109452 A232665 A178625 * A284911 A091130 A141447

Adjacent sequences: A350824 A350825 A350826 * A350828 A350829 A350830

Keyword

nonn,hard,more,base

Author

M. F. Hasler, Mar 01 2022

Status

approved