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 A046025 #31 Apr 06 2025 06:37:39
%S A046025 1,6,35,45,51,55,56,100,121,195,206,216,255,276,370,380,426,506,510,
%T A046025 511,710,741,800,825,871,930,975,1025,1060,1115,1140,1161,1270,1280,
%U A046025 1281,1311,1336,1361,1365,1381,1420,1421,1441,1490,1515,1696,1805,1875,1885
%N A046025 Numbers k such that 6*k+1, 12*k+1 and 18*k+1 are all primes.
%C A046025 Main entry for this sequence is A033502.
%C A046025 k is a Carmichael number generator giving C(k) = (6*k+1)*(12*k+1)*(18*k+1) = A382809(k).
%D A046025 R. K. Guy, Unsolved Problems in Number Theory, A13.
%D A046025 Ivan Niven, Herbert S. Zuckerman, and Hugh L. Montgomery, An Introduction to the Theory Of Numbers, Fifth Edition, Wiley NY 1991, page 83, problem #20.
%D A046025 Paulo Ribenboim, The Little Book of Bigger Primes, Springer-Verlag NY 2004. See p. 101.
%H A046025 Donovan Johnson, <a href="/A046025/b046025.txt">Table of n, a(n) for n = 1..10000</a>
%H A046025 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/CarmichaelNumber.html">Carmichael Number</a>.
%H A046025 <a href="/index/Ca#Carmichael">Index entries for sequences related to Carmichael numbers</a>.
%t A046025 Select[Range[2000],And@@PrimeQ[{6,12,18}#+1]&] (* _Harvey P. Dale_, May 26 2014 *)
%o A046025 (PARI) is(n)=isprime(6*n+1) && isprime(12*n+1) && isprime(18*n+1) \\ _Charles R Greathouse IV_, Jan 04 2022
%Y A046025 Cf. A033502, A002997, A382809.
%K A046025 nonn
%O A046025 1,2
%A A046025 _Eric W. Weisstein_
%E A046025 Better description from _Robert G. Wilson v_, Sep 27 2000