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A074169 Number of representations of n as a sum of two primes that are not congruent modulo 3. 2
0, 0, 0, 0, 1, 0, 0, 1, 1, 1, 0, 1, 0, 1, 1, 1, 0, 2, 0, 1, 1, 1, 0, 3, 0, 1, 0, 0, 0, 3, 0, 1, 1, 1, 0, 4, 0, 0, 1, 1, 0, 4, 0, 1, 1, 1, 0, 5, 0, 1, 0, 0, 0, 5, 0, 1, 0, 0, 0, 6, 0, 1, 1, 1, 0, 6, 0, 0, 1, 1, 0, 6, 0, 1, 1, 1, 0, 7, 0, 0, 1, 1, 0, 8, 0, 1, 0, 0, 0, 9, 0, 1, 0, 0, 0, 7, 0, 0, 1, 1, 0, 8, 0, 1, 1 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,18

LINKS

Table of n, a(n) for n=1..105.

EXAMPLE

18 can be written in two ways as the sum of two incongruent primes modulo 3: 18 = 5 + 13 (5 = 2 mod 3; 13 = 1 mod 3) and 18 = 7 + 11 (order of addition is ignored). Hence a(18) = 2.

MATHEMATICA

f[n_] := Module[{a, d, i}, a = {}; u = Floor[n/2]; For[i = 1, i <= u, i++, If[PrimeQ[i] && PrimeQ[n - i] && Mod[i, 3] != Mod[n - i, 3], a = Append[a, {n, i, n - i}]]]; a]; Table[Length[f[n]], {n, 1, 200}]

CROSSREFS

Cf. A078646, A078647, A078648.

Sequence in context: A243223 A034178 A317531 * A328458 A099362 A321378

Adjacent sequences:  A074166 A074167 A074168 * A074170 A074171 A074172

KEYWORD

nonn

AUTHOR

Joseph L. Pe, Dec 13 2002

STATUS

approved

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Last modified May 31 16:29 EDT 2020. Contains 334748 sequences. (Running on oeis4.)