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 A338266 #35 Jul 01 2021 01:42:25 %S A338266 3,7,3,17,3,19,2,19,3,5,3,43,2,7,3,19,2,5,2,17,3,7,3,167,2,7,3,11,3,3, %T A338266 2,19,3,2,3,67,2,2,3,17,3,17,2,7,2,5,2,211,2,7,3,7,3,11,3,13,2,3,2, %U A338266 139,2,2,3,31,3,19,2,5,3,5,2,109,2,5,3,2,2,3,2 %N A338266 Least prime p such that p*n is not a totient number. %C A338266 Zhang Ming-Zhi has shown that for every positive integer n, there is a prime p such that p*n is not a totient (see Reference and link, theorem 1). %C A338266 Differs from A282160, where multiplier p is not requested to be prime, for n = 6, 66, 80, 126, ... those indices where A282160(n) is not prime (see Example). %D A338266 Richard K. Guy, Unsolved Problems in Number Theory, 3rd Edition, Springer, 2004, Section B36, p. 139. %H A338266 Amiram Eldar, <a href="/A338266/b338266.txt">Table of n, a(n) for n = 1..10000</a> %H A338266 Zhang Ming-Zhi, <a href="https://doi.org/10.1006/jnth.1993.1014">On Nontotients</a>, J. Number Theory, Vol. 43, No. 2 (1993), pp. 168-172. %F A338266 a(A079695(n)) = 2. %e A338266 a(6) = 19 because 19 * 6 = 114 is not a totient number and 19 is the least prime with this property. Also 15 * 6 = 90 is not either a totient number, so A282160(6) = 15 that is not a prime number. %o A338266 (PARI) a(n) = my(p=2); while (istotient(p*n), p = nextprime(p+1)); p; \\ _Michel Marcus_, Oct 19 2020 %Y A338266 Cf. A000010, A002202, A061026, A071615, A079695, A282160. %K A338266 nonn %O A338266 1,1 %A A338266 _Bernard Schott_, Oct 19 2020