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 A063844 #14 Jun 02 2025 05:00:21
%S A063844 645,4369,13747,15709,88357,157641,642001,656601,1507963,2269093,
%T A063844 2313697,4101637,7428421,7429117,8388607,22669501,26296401,27218269,
%U A063844 27336673,28011001,32701297,34487601,36507801,37167361,47903701,54215161,71804161,72498253,74411131,82279741,86438857,86530621,93614521,96135601,97863529
%N A063844 Smith numbers which are also base-2 pseudoprimes.
%H A063844 Amiram Eldar, <a href="/A063844/b063844.txt">Table of n, a(n) for n = 1..10000</a>
%e A063844 645 is a member since 645=3*5*43, sum of digits of 645 is 6+4+5=15, sum of digits of prime factors = 3+5+4+3=15 and 2^644 (mod 645) == 1.
%t A063844 fQ[n_] := Block[{id = Sort@ IntegerDigits@ n, fid = Sort@ Flatten[ IntegerDigits@ Table[#[[1]], {#[[2]]}] & /@ FactorInteger@ n]}, While[ id[[1]] == 0, id = Drop[id, 1]]; While[ fid[[1]] == 0, fid = Drop[fid, 1]]; id != fid && Plus @@ id == Plus @@ fid]; k = 1; lst = {}; While[k < 10^8, If[!PrimeQ@ k && PowerMod[2, k-1, k] == 1, AppendTo[lst, k]]; k++]; Select[ lst, fQ]
%Y A063844 Intersection of A001567 and A006753.
%K A063844 base,nonn
%O A063844 1,1
%A A063844 _Shyam Sunder Gupta_, Aug 25 2001