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 A078330 #24 Feb 16 2025 08:32:48 %S A078330 3,31,43,67,71,79,103,131,139,191,223,239,283,311,367,419,431,439,443, %T A078330 499,599,607,619,643,647,659,683,743,787,823,827,907,947,971,1031, %U A078330 1039,1087,1091,1103,1163,1223,1259,1399,1427,1447,1499,1511,1543,1559,1571 %N A078330 Primes p such that mu(p-1) = -1, where mu is the Moebius function; that is, p-1 is squarefree and has an odd number of prime factors. %H A078330 Amiram Eldar, <a href="/A078330/b078330.txt">Table of n, a(n) for n = 1..10000</a> %H A078330 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/MoebiusFunction.html">Moebius Function</a>. %e A078330 31 is in the sequence because 31 is a prime and mu(30) = -1. %e A078330 37 is not in the sequence because, although 37 is prime, mu(36) = 0. %t A078330 Select[Prime[Range[400]], MoebiusMu[# - 1] == -1 &] (* from _T. D. Noe_ *) %o A078330 (PARI) j=[]; forprime(n=1,2000,if(moebius(n)==moebius(n-1),j=concat(j,n))); j %Y A078330 Cf. A008683, A049092 (primes p with mu(p-1) = 0), A088179 (primes p with mu(p-1) = 1), A089451 (mu(p-1) for prime p). %K A078330 easy,nonn %O A078330 1,1 %A A078330 _Shyam Sunder Gupta_, Nov 21 2002