This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
k=17; Do[p=Prime[n]; f=(k^p-5^p)/(k-5); If[ PrimeQ[f], Print[p] ], {n,1,100}]
is(n)=isprime((17^n-5^n)/12) \\ Charles R Greathouse IV, Feb 17 2017
k=18; Do[p=Prime[n]; f=(k^p-5^p)/(k-5); If[ PrimeQ[f], Print[p] ], {n,1,100}]
is(n)=isprime((18^n-5^n)/13) \\ Charles R Greathouse IV, Feb 17 2017
k=19; Do[p=Prime[n]; f=(k^p-5^p)/(k-5); If[ PrimeQ[f], Print[p] ], {n,1,100}]
is(n)=isprime((19^n-5^n)/14) \\ Charles R Greathouse IV, Feb 17 2017
k=13; Do[p=Prime[n]; f=(k^p-5^p)/(k-5); If[ PrimeQ[f], Print[p] ], {n,1,100}]
is(n)=isprime((13^n-5^n)/8) \\ Charles R Greathouse IV, Feb 17 2017
k=14; Do[p=Prime[n]; f=(k^p-5^p)/(k-5); If[ PrimeQ[f], Print[p] ], {n,1,200}]
is(n)=isprime((14^n-5^n)/9) \\ Charles R Greathouse IV, Feb 17 2017
k=8; Do[p=Prime[n]; f=(k^p+5^p)/(k+5); If[ PrimeQ[f], Print[p] ], {n,1,100}]
is(n)=isprime((8^n+5^n)/13) \\ Charles R Greathouse IV, Feb 17 2017
k=14; Do[p=Prime[n]; f=(k^p+5^p)/(k+5); If[ PrimeQ[f], Print[p] ], {n,1,100}]
is(n)=isprime((14^n+5^n)/19) \\ Charles R Greathouse IV, Feb 17 2017
Select[ Prime[ Range[100000] ], PrimeQ[ (7^# + 6^#)/13 ]& ]
is(n)=ispseudoprime((7^n+6^n)/13) \\ Charles R Greathouse IV, Feb 17 2017
is(n)=ispseudoprime((16^n+15^n)/31) \\ Charles R Greathouse IV, May 22 2017
a(10) = 53 because (10^p + 11^p)/21 is composite for all p < 53 and prime for p = 53.
lmt = 4200; f[n_] := Block[{p = 2}, While[p < lmt && !PrimeQ[((n + 1)^p + n^p)/(2n + 1)], p = NextPrime@ p]; If[p > lmt, 0, p]]; Do[Print[{n, f[n] // Timing}], {n, 1000}] (* Robert G. Wilson v, Dec 01 2014 *)
a(n)=forprime(p=3, , if(ispseudoprime((n^p+(n+1)^p)/(2*n+1)), return(p)))
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