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 A177266 #17 Jun 28 2024 08:51:00
%S A177266 1,4,1,5,8,1,4,6,2,1,2,4,4,2,1,8,2,4,2,2,1,11,8,1,11,2,1,1,14,20,8,4,
%T A177266 14,18,2,1,2,13,11,18,23,24,16,8,1,10,22,6,16,14,20,6,16,2,1,17,29,16,
%U A177266 8,17,25,4,2,25,29,1,30,16,2,18,16,8,32,16,2,18,2,1,23,32,4,2,22
%N A177266 Triangle read by rows: R(n,k) = 2^(semiprime(n)-semiprime(k)) mod semiprime(n).
%e A177266 Triangle begins:
%e A177266 1,
%e A177266 4, 1,
%e A177266 5, 8, 1,
%e A177266 4, 6, 2, 1,
%e A177266 2, 4, 4, 2, 1,
%e A177266 8, 2, 4, 2, 2, 1,
%t A177266 Table[PowerMod[2, #[[n]] - #[[;;n]], #[[n]]], {n, Length[#]}] & [Select[Range[50], PrimeOmega[#] == 2 &]] (* _Paolo Xausa_, Jun 28 2024 *)
%o A177266 (PARI) trg(nn) = {semip = select(n->bigomega(n) == 2, vector(nn, i, i)); for (n = 1, #semip, for (k = 1, n, print1(2^(semip[n] - semip[k]) % semip[n], ", ");); print(););} \\ _Michel Marcus_, Sep 11 2013
%Y A177266 Cf. A000079, A001358, A173622, A174479, A176066, A181615.
%K A177266 nonn,tabl
%O A177266 1,2
%A A177266 _Juri-Stepan Gerasimov_, Dec 10 2010
%E A177266 Corrected by _D. S. McNeil_, Dec 10 2010