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Smallest prime number that begins a prime gap of at least 2n.
4

%I #15 Sep 06 2024 14:43:16

%S 3,7,23,89,113,113,113,523,523,887,1129,1327,1327,1327,1327,1327,1327,

%T 9551,15683,15683,15683,15683,19609,19609,19609,19609,31397,31397,

%U 31397,31397,31397,31397,31397,31397,31397,31397,155921,155921,155921,155921

%N Smallest prime number that begins a prime gap of at least 2n.

%H Amiram Eldar, <a href="/A100964/b100964.txt">Table of n, a(n) for n = 1..775</a>

%F a(n) = prime(A144309(n)). - _Michel Marcus_, Nov 02 2013

%e a(5) = a(6) = a(7) = 113 because there is a gap of 14 between 113 and 127.

%t k=1; Table[While[Prime[k+1]-Prime[k] < 2n, k++ ]; Prime[k], {n, 48}]

%o (PARI) lista(pmax) = {my(k = 1, prv = 2, m = 2, kprv = 2); forprime(p = 3, pmax, k++; if(p - prv >= m, for(i = 1, (p - prv - m)/2 + 1, print1(prv, ", ")); m = p - prv + 2; kprv = k); prv = p);} \\ _Amiram Eldar_, Sep 06 2024

%Y Cf. A000230, A002386, A005250, A144309.

%K nonn

%O 1,1

%A _T. D. Noe_, Nov 23 2004