OFFSET
2,48
COMMENTS
If the Goldbach Conjecture is true, this sequence is defined for n >= 2.
FORMULA
EXAMPLE
For n=2, 2n=4 = 2+2, there is one prime, which is 3, between 2 and 4. So a(2)=1;
...
For n=8, 2n=16 = 13+3, there is no prime between 13 and 16. So a(8)=0;
...
For n=49, 2n=98 = 79+19, there are three primes, 83, 89, and 97 between 79 and 98 such that the difference of 98 and these primes, 15, 9, and 1 respectively, are not prime. So a(49)=3.
MATHEMATICA
Table[n2 = n*2; p = NextPrime[n2]; ct = 0; While[p = NextPrime[p, -1]; ! PrimeQ[n2 - p], ct++]; ct, {n, 2, 88}]
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Lei Zhou, Aug 01 2018
STATUS
approved