A154726 Triangle read by rows in which row n lists: n, in the center of the row and the pairs of prime numbers that are equidistant to n, as shown below in the example.

1, 2, 3, 3, 4, 5, 3, 5, 7, 5, 6, 7, 3, 7, 11, 3, 5, 8, 11, 13, 5, 7, 9, 11, 13, 3, 7, 10, 13, 17, 3, 5, 11, 17, 19, 5, 7, 11, 12, 13, 17, 19, 3, 7, 13, 19, 23, 5, 11, 14, 17, 23, 7, 11, 13, 15, 17, 19, 23, 3, 13, 16, 19, 29, 3, 5, 11, 17, 23, 29

Offset: 1

Author

Omar E. Pol, Jan 14 2009

Keywords

• easy
• nonn
• tabf

Examples

			Triangle begins:
                       1
                       2
                       3
                    3  4  5
                 3  .  5  .  7
              .  .  5  6  7  .  .
           3  .  .  .  7  .  .  . 11
        3  .  5  .  .  8  .  . 11  . 13
     .  .  5  .  7  .  9  . 11  . 13  .  .
  3  .  .  .  7  .  . 10  .  . 13  .  .  . 17
		

Links

• Nathaniel Johnston, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000040, A154720, A154721, A154722, A154723, A154724, A154725, A154727.

Programs

Maple

for n from 1 to 10 do for k from 1 to 2*n-1 do if(k=n or (isprime(k) and isprime(2*n-k)))then print(k):fi:od:od: # Nathaniel Johnston, Apr 18 2011

Mathematica

Select[Flatten@Table[If[k == n  || ( PrimeQ[k] && PrimeQ[2 n - k]), k, 0], {n, 10}, {k, 2 n - 1}] , # > 0 &] (* Robert Price, Apr 26 2025 *)

Extensions

a(31)-a(70) from Nathaniel Johnston, Apr 18 2011