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 A372186 #9 Apr 21 2024 19:10:06
%S A372186 333,741,1659,1749,2505,2706,2730,4221,4437,4851,5625,6447,7791,7977,
%T A372186 8229,8250,9216,10833,12471,13950,14028,15147,16002,17667,18207,18246,
%U A372186 19152,20517,23400,23421,23961,25689,26247,28587,28608,30363,31584,34167,36330,36378
%N A372186 Numbers m such that 20*m + 1, 80*m + 1, 100*m + 1, and 200*m + 1 are all primes.
%C A372186 If m is a term, then (20*m + 1) * (80*m + 1) * (100*m + 1) * (200*m + 1) is a Carmichael number (A002997). These are the Carmichael numbers of the form U_{4,4}(m) in Nakamula et al. (2007).
%C A372186 The corresponding Carmichael numbers are 393575432565765601, 9648687289456956001, 242412946401534283201, ...
%H A372186 Amiram Eldar, <a href="/A372186/b372186.txt">Table of n, a(n) for n = 1..10000</a>
%H A372186 Ken Nakamula, Hirofumi Tsumura, and Hiroaki Komai, <a href="https://arxiv.org/abs/math/0702410">New polynomials producing absolute pseudoprimes with any number of prime factors</a>, arXiv:math/0702410 [math.NT], 2007.
%e A372186 333 is a term since 20*333 + 1 = 6661, 80*333 + 1 = 26641, 100*333 + 1 = 33301, and 200*333 + 1 = 66601 are all primes.
%t A372186 q[n_] := AllTrue[{20, 80, 100, 200}, PrimeQ[# * n + 1] &]; Select[Range[40000], q]
%o A372186 (PARI) is(n) = isprime(20*n + 1) && isprime(80*n + 1) && isprime(100*n + 1) && isprime(200*n + 1);
%Y A372186 Cf. A002997, A318646, A372189.
%Y A372186 Similar sequences: A046025, A257035, A206024, A206349, A372187, A372188.
%K A372186 nonn,easy
%O A372186 1,1
%A A372186 _Amiram Eldar_, Apr 21 2024