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
Examples
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.
Crossrefs
Programs
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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
Comments