cp's OEIS Frontend

A139074 a(n) = smallest prime p such that p!/n + 1 is prime, or 0 if no such prime exists.

%I A139074 #18 Sep 24 2013 09:23:08
%S A139074 2,2,3,5,7,3,11,7,26737,5,13,5
%N A139074 a(n) = smallest prime p such that p!/n + 1 is prime, or 0 if no such prime exists.
%C A139074 For the corresponding primes p see A139075.
%C A139074 a(9)>5000, a(13)>5000, a(22)>5000, a(23) = 1579. - _Andrew V. Sutherland_, Apr 21 2008, Apr 22 2008
%C A139074 a(10)=5,   a(11)=13, a(12)=5
%C A139074 a(14)=17,  a(15)=7,  a(16)=13,  a(17)=43, a(18)=7,
%C A139074 a(19)=31,  a(20)=5,  a(21)=7
%C A139074 a(24)=7,   a(25)=47, a(26)=17,  a(27)=17, a(28)=7,
%C A139074 a(29)=241, a(30)=5,  a(31)=61,  a(32)=11, a(33)=17,
%C A139074 a(34)=17,  a(35)=29, a(36)=11,  a(37)=61, a(38)=103,
%C A139074 a(39)=89,  a(40)=7,  a(41)=131, a(42)=11, a(43)=71,
%C A139074 a(44)=13,  a(45)=7,  a(46)=43,  a(47)=73, a(48)=67,
%C A139074 a(49)=347, a(50)=31, a(51)=19,  a(52)=17, a(53)=347,
%C A139074 a(54)=11,  a(55)=13, a(56)=13,  a(57)=31, a(58)=73,
%C A139074 a(59)=641, a(60)=5
%C A139074 a(23) = 1579. - _Andrew V. Sutherland_, Apr 11 2008.
%C A139074 Smallest daughter factorial prime p of order n, i.e. smallest prime of the form (p!+n)/n where p is prime.
%C A139074 For smallest mother factorial prime p of order n see A139075
%C A139074 For smallest father factorial prime p of order n see A139207
%C A139074 For smallest son factorial prime p of order n see A139206
%C A139074 Summary added by Robert Price, Nov 25 2010:
%C A139074 a(1:20)=2,2,3,5,7,3,11,7,26737,5,13,5,>60000,17,7,13,43,7,31,5
%C A139074 a(21:40)=7,>60000,1579,7,47,17,17,7,241,5,61,11,17,17,29,11,61,103,89,7
%C A139074 a(41:60)=131,11,71,13,7,43,73,67,347,31,19,17,347,11,13,13,31,73,641,5
%C A139074 a(61:80)=89,31,13,13,17,11,71,19,131,7,151,7,>10000,641,73,43,17,331,113,11
%C A139074 a(81:100)=13,67,>10000,7,1999,89,31,11,>10000,19,19,31,607,71,61,11,761,23,>10000,83
%e A139074 a(1) = 2 because 2 is the first prime and 2!/1 + 1 = 3 is prime
%e A139074 a(2) = 2 because 2 is the first prime and 2!/2 + 1 = 2 is prime
%e A139074 a(3) = 3 because 3!/3 + 1 = 3 is prime
%t A139074 a = {}; Do[k = 1; While[ ! PrimeQ[(Prime[k]! + n)/n], k++ ]; AppendTo[a, Prime[k]], {n, 1, 8}]; a
%Y A139074 Cf. A082672, A089085, A089130, A117141, A007749, A139056-A139066, A020458, A139068, A137390, A139070-A139075, A136019, A136020, A136026, A136027.
%K A139074 more,nonn
%O A139074 1,1
%A A139074 _Artur Jasinski_, Apr 08 2008, Apr 21 2008
%E A139074 a(9)-a(12) by _Robert Price_, Dec 19 2010