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A238205
a(n) is the smallest prime such that 2n=p1+p2*p3 where Max(p1,p2,p3)=a(n) and p1, p2 p3 are odd primes.
1
3, 5, 7, 5, 5, 7, 7, 7, 5, 5, 7, 13, 11, 7, 7, 7, 11, 11, 13, 13, 7, 7, 7, 11, 11, 11, 17, 11, 13, 13, 13, 19, 13, 13, 11, 11, 11, 23, 11, 13, 17, 13, 13, 13, 19, 13, 13, 19, 17, 19, 19, 19, 29, 23, 23, 17, 11, 11, 11, 17, 11, 13, 17, 17, 19, 23, 19, 13, 13, 13
OFFSET
6,1
COMMENTS
a(n) is defined for integers n >= 6.
EXAMPLE
n=6, 2n=12=3+3*3, Max[3,3,3]=3, so a(6)=3;
n=7, 2n=12=5+3*3, Max[5,3,3]=5, so a(7)=5;
..
n=10, 2n=20=11+3*3=5+5*3, Max[11,3,3]=11, Max[5,5,3]=5, Min[11,5]=5, so a(10)=5.
MATHEMATICA
Table[p = 2; r = n; While[p = NextPrime[p]; m = n - p; m >= 9, f = Transpose[FactorInteger[m]]; If[(Total[f[[2]]] == 2)&&(f[[1, 1]]>2), s = Max[Max[f[[1]]], p]; If[r > s, r = s]]]; r, {n, 12, 150, 2}]
CROSSREFS
Cf. A002375.
Sequence in context: A279321 A254863 A085965 * A186702 A141710 A279399
KEYWORD
nonn,easy
AUTHOR
Lei Zhou, Feb 20 2014
STATUS
approved