

A185446


Least prime such that whenever 2*a(n) = p+q with p and q prime, one has p,q > prime(n).


4



3, 19, 19, 61, 61, 151, 151, 173, 173, 601, 677, 677, 677, 677, 691, 691, 691, 1321, 1321, 1321, 1321, 1321, 1321, 1321, 1321, 1321, 4801, 4801, 4801, 4801, 4801, 4801, 4801, 6781, 6781, 24001, 24001, 24001, 24001, 24001, 24001, 24001, 24001, 51869, 51869, 51869, 51869, 51869, 97151, 97151
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OFFSET

1,1


LINKS



FORMULA



EXAMPLE

For n=1, the least prime P such that 2P cannot be written as the sum of two primes of which at least one is <= prime(1)=2, is obviously P=3.
For n=2, we have a(2)=19, which is such that 2*19 can be written as the sum of primes only as 7+31 and 19+19, where no prime <= prime(2)=3 occurs. For smaller primes we have 2*17=3+31, 2*13=3+23, 2*11=3+19, 2*7=3+11, 2*5=3+5 (always using 3=prime(2)), and of course 3 and 2 are excluded, too.


PROG

(Sage)
pn = nth_prime(n)
twoprimes = lambda n: ((p, np) for p in primes(n+1) if is_prime(np))
return next(ap for ap in Primes() if all(p>pn and q>pn for p, q in twoprimes(2*ap))) # D. S. McNeil, Feb 04 2011


CROSSREFS



KEYWORD

nonn


AUTHOR



STATUS

approved



