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%I #34 Jun 10 2018 16:05:24
%S 2,7,23,59,71,71,71,3643,62939,292627,292627,1089427,2374649,2374649
%N a(n) is the smallest prime dividing n numbers of the form k! + 1.
%C Note that were the title altered to instead count the numbers k for which p divides k!+1, then a(2) would be 2 rather than 7 (as 0!+1=1!+1).
%C Ties arise for the following list of values: 3, 5, 11, 19, 61, 661, 2267, 3163, 3541, 6529, 9697, 12227, 40751, 46687, 51347, 59447, 69493, 72077, 72923, 83579, 141907, 167267, 201667 and 212207 (and were not sought beyond a(11)).
%C Search for a(15) completed through the 260000th prime. - _James G. Merickel_, Jan 16 2014
%C a(15) > 1.1*10^8. - _Giovanni Resta_, Jun 10 2018
%H Wikipedia, <a href="http://en.wikipedia.org/wiki/Wilson%27s_theorem">Wilson's theorem</a>
%e 71 divides 7!+1, 9!+1, 19!+1, 51!+1, 61!+1, 63!+1, and of course 70!+1 (Wilson's Theorem). Since a(4)=59 and 61 and 67 do not enter in, 71=a(n) for n=5 to 7.
%o (PARI)
%o {
%o \\ y is an arbitrary value. \\
%o rec=0;y=10^7;z=primepi(y);a=vector(z,x,1);
%o b=vector(z);q=vector(z,x,prime(x));i=1;
%o for(k=1,z,
%o for(r=i,q[k],
%o for(j=k,z,
%o a[j]*=r;a[j]%=q[j];
%o if(a[j]==q[j]-1,b[j]++));
%o while(b[j]>rec,
%o rec++;print1(q[j]", ")));
%o i=q[k]+1)
%o }
%Y Cf. A051301, A230459
%K nonn,hard,more
%O 1,1
%A _James G. Merickel_, Oct 15 2013
%E a(12)-a(14) added (with a search limit for a(15) in Comments) by _James G. Merickel_, Jan 16 2014
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