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A124867
Numbers that are the sum of 3 distinct primes.
11
10, 12, 14, 15, 16, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81
OFFSET
1,1
COMMENTS
(Conjecture) Every number n > 17 is the sum of 3 distinct primes. Natural numbers that are not the sum of 3 distinct primes are listed in A124868.
A125688(a(n)) > 0. - Reinhard Zumkeller, Nov 30 2006
EXAMPLE
The first three primes are 2, 3, 5, and 2 + 3 + 5 = 10, so 10 is in the sequence. No smaller integer is in the sequence.
5 + 5 + 5 = 15, but note also 3 + 5 + 7 = 15, so 15 is in the sequence.
Although 13 = 3 + 3 + 7 = 3 + 5 + 5, both of those repeat primes, so 13 is not in the sequence.
MATHEMATICA
threePrimes[n_] := Module[{p, q, r}, {p, q, r} /. Solve[n == p + q + r && p < q < r, {p, q, r}, Primes]];
Reap[For[n = 10, n <= 100, n++, sol = threePrimes[n]; If[MatchQ[sol, {{_, _, _}..}], Print[n, " ", sol[[1]]]; Sow[n]]]][[2, 1]] (* Jean-François Alcover, Apr 26 2020 *)
has3DistPrimesPart[n_] := Length[Select[IntegerPartitions[n, {3}], Length[Union[#]] == 3 && Union[PrimeQ[#]] == {True} &]] > 0; Select[Range[100], has3DistPrimesPart] (* Alonso del Arte, Apr 26 2020 *)
Union[Total/@Subsets[Prime[Range[20]], {3}]] (* Harvey P. Dale, Feb 06 2024 *)
PROG
(PARI) a(n)=if(n>5, n+12, [10, 12, 14, 15, 16][n]) \\ Charles R Greathouse IV, Aug 26 2011
CROSSREFS
Cf. A124868 (not the sum of 3 distinct primes), A068307, A125688.
Sequence in context: A331276 A230597 A330904 * A199991 A161598 A122426
KEYWORD
nonn,easy
AUTHOR
Alexander Adamchuk, Nov 11 2006
STATUS
approved