OFFSET
1,1
LINKS
Lei Zhou, Table of n, a(n) for n = 1..10000
EXAMPLE
4 is the smallest number that can be written in only one way as the sum of two primes or doubled primes, 4=2+2. So a(1)=4;
6 = 2+2*2 = 3+3, two ways, so a(2)=6;
...
33 = 2+31 = 2*2+29 = 7+2*13 = 2*5+23 = 11+2*11 = 2*7+19, 6 ways. And all numbers smaller than 33 can only be split in 5 or fewer ways. So a(6)=33.
MATHEMATICA
target = 55; n = 3; a = {}; sc = 0; Do[AppendTo[a, 0], {i, 1, target}]; While[sc < target, n++; ct = 0; Do[If[((PrimeQ[i]) || (PrimeQ[i/2])) && ((PrimeQ[n - i]) || (PrimeQ[(n - i)/2])), ct++], {i, 2, Floor[n/2]}]; If[ct<=target, If[a[[ct]] == 0, a[[ct]] = n; sc++]]]; a
CROSSREFS
KEYWORD
nonn
AUTHOR
Lei Zhou, Feb 21 2014
STATUS
approved