A065305 Triangular array giving means of two odd primes: T(n,k) = (n-th prime + k-th prime)/2, n >= k >= 2.

3, 4, 5, 5, 6, 7, 7, 8, 9, 11, 8, 9, 10, 12, 13, 10, 11, 12, 14, 15, 17, 11, 12, 13, 15, 16, 18, 19, 13, 14, 15, 17, 18, 20, 21, 23, 16, 17, 18, 20, 21, 23, 24, 26, 29, 17, 18, 19, 21, 22, 24, 25, 27, 30, 31, 20, 21, 22, 24, 25, 27, 28, 30, 33, 34, 37, 22, 23, 24, 26, 27, 29, 30

Offset: 2

Author

Klaus Strassburger (strass(AT)ddfi.uni-duesseldorf.de), Oct 29 2001

Keywords

• easy
• nonn
• tabl

Examples

			3; 4,5; 5,6,7; 7,8,9,11; ...
		

Links

• Reinhard Zumkeller, First 125 rows of triangle, flattened
• Index entries for sequences related to Goldbach conjecture

Crossrefs

Cf. A065306.

a(n, k) = A065342(n, k)/2 [but note different offsets]

Cf. A098090 (left edge), A065091 (right edge), A000040.

Programs

Haskell

import Data.List (inits)
a065305 n k = a065305_tabl !! (n-2) !! (k - 1)
a065305_row n = a065305_tabl !! (n-2)
a065305_tabl = zipWith (map . (flip div 2 .) . (+))
                       a065091_list $ tail $ inits a065091_list
-- Reinhard Zumkeller, Aug 02 2015, Jan 30 2012

Maple

seq(seq((ithprime(i)+ithprime(j))/2,j=2..i),i=2..20)