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.
%I A072164 #22 Feb 16 2025 08:32:46 %S A072164 2,3,4,7,11,17,106,120,1907,7918 %N A072164 Numbers k >= 1 such that f(k) = k^k - (k-1)^(k-1) is prime. %C A072164 Enoch Haga proposed studying the primality of f(k) and he already knew the first 4 solutions. C. Rivera found the next four solutions using Ubasic and the last one using PRIMEFORM. Currently f(1907) is only a probable prime number, according to PRIMEFORM. %C A072164 No other k < 25000. - _T. D. Noe_, Jun 12 2008 %H A072164 C. Rivera, <a href="http://www.primepuzzles.net/puzzles/puzz_185.htm">Puzzle 185</a> %H A072164 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/PowerDifferencePrime.html">Power Difference Prime</a> %H A072164 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/IntegerSequencePrimes.html">Integer Sequence Primes</a> %e A072164 2^2 - 1^1 = 3 is prime. %t A072164 Select[Range[2, 200], PrimeQ[ #^#-(#-1)^(#-1)]&] (* _T. D. Noe_, Jun 12 2008 *) %o A072164 (PARI) isok(k) = ispseudoprime(k^k - (k-1)^(k-1)); \\ _Jinyuan Wang_, Mar 19 2020 %Y A072164 Cf. A007781 (n^n-(n-1)^(n-1)). Equals A140669 + 1. %K A072164 nonn,hard,more %O A072164 1,1 %A A072164 _Carlos Rivera_, Jun 28 2002 %E A072164 7918 found by _Henri Lifchitz_ in 2001, contributed by _Eric W. Weisstein_, Nov 29 2005