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 A308270 #7 May 26 2019 15:00:08 %S A308270 2,5,307,277 %N A308270 Smallest prime with E-irregularity index n. %C A308270 Smallest prime p such that A308243(i) = n, where i is the index of p in A000040. %C A308270 E-regular primes have E-irregularity index 0, so a(0) = 2, since 2 is the smallest E-regular prime (A092217). %C A308270 Does such a prime exist for every n? %C A308270 a(4) > 2003 if it exists. %H A308270 R. Ernvall and T. Metsänkylä, <a href="https://doi.org/10.1090/S0025-5718-1978-0482273-9">Cyclotomic invariants and E-irregular primes</a>, Mathematics of Computation 32 (1978), 617-629. %o A308270 (PARI) a000364(n) = subst(bernpol(2*n+1), 'x, 1/4)*4^(2*n+1)*(-1)^(n+1)/(2*n+1) \\ after _Charles R Greathouse IV_ in A000364 %o A308270 a308243(n) = my(p=prime(n), e=2, i=0); while(e <= p-3, if(a000364(e)%p==0, i++); e=e+2); i %o A308270 a(n) = for(x=1, oo, if(a308243(x)==n, return(prime(x)))) %Y A308270 Cf. A000040, A061576, A092217, A308243. %K A308270 nonn,hard,more %O A308270 0,1 %A A308270 _Felix Fröhlich_, May 17 2019