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 A154720 #17 Apr 26 2025 15:27:11
%S A154720 1,1,2,3,1,0,3,0,5,1,0,3,4,5,0,7,0,0,3,0,5,0,7,0,0,1,0,0,0,5,6,7,0,0,
%T A154720 0,11,1,0,3,0,0,0,7,0,0,0,11,0,13,0,0,3,0,5,0,0,8,0,0,11,0,13,0,0,1,0,
%U A154720 0,0,5,0,7,0,9,0,11,0,13,0,0,0,17
%N A154720 Triangle read by rows in which row n lists 2n-1 terms: n, in the center of the row and all the pairs of noncomposite numbers equidistant to n, with 0's inserted, as shown below in the example.
%H A154720 Nathaniel Johnston, <a href="/A154720/b154720.txt">Table of n, a(n) for n = 1..10000</a>
%e A154720 Triangle begins:
%e A154720 1
%e A154720 1 2 3
%e A154720 1 0 3 0 5
%e A154720 1 0 3 4 5 0 7
%e A154720 0 0 3 0 5 0 7 0 0
%e A154720 1 0 0 0 5 6 7 0 0 0 11
%e A154720 1 0 3 0 0 0 7 0 0 0 11 0 13
%e A154720 0 0 3 0 5 0 0 8 0 0 11 0 13 0 0
%e A154720 1 0 0 0 5 0 7 0 9 0 11 0 13 0 0 0 17
%e A154720 1 0 3 0 0 0 7 0 0 10 0 0 13 0 0 0 17 0 19
%p A154720 isnotcomp:=proc(n)return (n=1 or isprime(n)) end:
%p A154720 for n from 1 to 10 do for k from 1 to 2*n-1 do if(k=n or (isnotcomp(k) and isnotcomp(2*n-k)))then print(k):else print(0):fi:od:od: # _Nathaniel Johnston_, Apr 18 2011
%t A154720 Flatten@Table[If[k == n || ( !CompositeQ[k] && !CompositeQ[2 n - k]), k, 0], {n, 10}, {k, 2 n - 1}] (* _Robert Price_, Apr 26 2025 *)
%Y A154720 Cf. A000040, A008578, A154721-A154727.
%K A154720 easy,nonn,tabf
%O A154720 1,3
%A A154720 _Omar E. Pol_, Jan 14 2009