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 A353221 #21 May 05 2022 08:59:13 %S A353221 3581761,5173169,5968873,23872213,36974341,53711113,107023281, %T A353221 427294141,490950461,526359289,546649741,550230409,753532781, %U A353221 803264281,836683849,1115578101,1168492417,1193557093,1540454761,1632785701,2129304997,2295209281,2677147201 %N A353221 Squarefree base-2 Fermat pseudoprimes divisible by a Wieferich prime. %C A353221 Subsequence of A001567. %C A353221 The least term that is divisible by both 1093 and 3511 is a(799) = 7015325908501 = 937 * 1093 * 1951 * 3511. - _Amiram Eldar_, May 05 2022 %H A353221 Amiram Eldar, <a href="/A353221/b353221.txt">Table of n, a(n) for n = 1..10000</a> %H A353221 PrimeGrid, <a href="http://www.primegrid.com/server_status_subprojects.php">Subproject status</a>. %e A353221 3581761 = 29 * 113 * 1093, so it is a base-2 pseudoprime divisible by the Wieferich prime 1093 and is squarefree. %o A353221 (PARI) /* The following program is valid up to the current search bound for Wieferich primes, about 10^19 as of May 03 2022 (cf. PrimeGrid); the program may miss terms above that bound if there is another Wieferich prime */ %o A353221 forcomposite(c=1, , if(Mod(2, c)^(c-1)==1, if(Mod(c, 1093)==0 || Mod(c, 3511)==0, if(issquarefree(c), print1(c, ", "))))) %Y A353221 Cf. A001220, A001567, A158358, A219346, A247830, A247831, A295740. %K A353221 nonn %O A353221 1,1 %A A353221 _Felix Fröhlich_, May 01 2022