A294186 Number of distinct greater twin primes which are in Goldbach partitions of 2n.

0, 0, 0, 1, 2, 2, 1, 2, 3, 2, 2, 4, 3, 1, 3, 2, 2, 5, 3, 0, 4, 3, 2, 5, 5, 1, 4, 3, 1, 5, 3, 2, 6, 3, 0, 6, 5, 2, 6, 6, 0, 6, 5, 1, 6, 5, 1, 4, 3, 0, 7, 5, 2, 5, 6, 2, 9, 7, 1, 8, 6, 0, 6, 4, 0, 8, 5, 1, 3, 7, 2, 9, 7, 0, 7, 5, 2, 9, 6, 0, 9, 5, 0, 7, 11, 1, 6, 6

Offset: 1

Author

Marcin Barylski, Feb 11 2018

Keywords

• nonn

Comments

Tomas Oliveira e Silva in 2012 experimentally confirmed that all even numbers <= 4*10^18 have at least one Goldbach partition (GP) with a prime 9781 or less. Detailed examination of all even numbers < 10^6 showed that the most popular prime in all GPs is 3 (78497 occurrences), then 5 (70328), then 7 (62185), then 11 (48582), then 13 (40916), then 17 (31091), then 19 (29791) - all these primes are twin primes. These results gave rise to a hypothesis that twin primes should be rather frequent in GP, especially those relatively small.

Further empirical experiments demonstrated, surprisingly, there are in general two categories of even numbers n: category 1 - with 0, 1, or 2 distinct greater twin primes in all GPs(n), and category 2 - with fast increasing number of distinct greater twin primes in GPs(n).

Is a(n) = A294185(n-1)? - R. J. Mathar, Mar 22 2024

Examples

			a(5)=2 because 2*5=10 has two ordered Goldbach partitions: 3+7 and 5+5. 5 is a greater twin prime (because 3 and 5 are twin primes), 7 is a greater twin prime (because 5 and 7 are twin primes).
		

Links

• Marcin Barylski, Plot of first 20000 elements of the A294186
• Marcin Barylski, C++ program for generating A294186
• Tomas Oliveira e Silva, Goldbach conjecture verification

Crossrefs

Cf. A002372 (number of ordered Goldbach partitions), A006512 (greater of twin primes), A294185, A295424.

Programs

PARI

isgtwin(p) = isprime(p) && isprime(p-2);
a(n) = {vtp = []; forprime(p = 2, n, if (isprime(2*n-p), if (isgtwin(p), vtp = concat(vtp, p)); if (isgtwin(2*n-p), vtp = concat(vtp, 2*n-p)););); #Set(vtp);} \\ Michel Marcus, Mar 01 2018