A178953 Indices n such that 2*prime(n) cannot be written as a sum of two distinct prime(n-k) and prime(n+k).

1, 2, 4, 8, 9, 14, 15, 21, 22, 29, 30, 35, 38, 46, 48, 49, 50, 52, 53, 57, 58, 60, 61, 62, 65, 66, 90, 91, 95, 96, 97, 99, 114, 120, 121, 122, 123, 124, 125, 128, 145, 146, 149, 153, 154, 163, 176, 179, 180, 186, 187, 189, 191, 192, 197

Offset

1,2

Comments

Snapshots: a(1000) = 6922, a(2000) = 16376, a(3000) = 25951, a(4000) = 37266, a(5000) = 51926, a(6000) = 69928. - R. J. Mathar, Jan 08 2011

Links

Reinhard Zumkeller, Table of n, a(n) for n = 1..500

Formula

A178609(a(n))=0.

Maple

A178609 := proc(n) for k from n-1 to 0 by -1 do if ithprime(n-k)+ithprime(n+k)=2*ithprime(n) then return k; end if; end do: end proc:
for n from 1 to 200 do if A178609(n) = 0 then printf("%d, ", n) ; end if; end do: # R. J. Mathar, Jan 05 2011

Mathematica

A178609[n_] := For[k = n-1, k >= 0, k--, If[Prime[n-k] + Prime[n+k] == 2*Prime[n], Return[k]]]; Reap[For[n = 1, n <= 200, n++, If[A178609[n] == 0, Sow[n]]]][[2, 1]] (* Jean-François Alcover, Feb 13 2018, after R. J. Mathar *)

Prog

(Haskell)
a178953 n = a178953_list !! (n-1)
a178953_list = filter ((== 0) . a178609) [1..]
-- Reinhard Zumkeller, Jan 30 2014

Crossrefs

Cf. A178609, A071681, A178954.

Sequence in context: A115813 A326672 A048300 * A182653 A347202 A036349

Adjacent sequences: A178950 A178951 A178952 * A178954 A178955 A178956

Keyword

nonn

Author

Juri-Stepan Gerasimov, Jan 02 2011

Status

approved