OFFSET
1,1
COMMENTS
This is the second row of the infinite array: A(k,n) = Smallest odd prime q such that pq+k is semiprime, where p is the n-th odd prime. The odd semiprimes arising begin: 35, 57, 51, 35, 57, 93, 87, 249, 301, 205. The above A(k,n) = Smallest odd prime q such that pq+k is semiprime, where p is the n-th odd prime, is the 2nd plane of the infinite 3-D array: A(j,k,n) = Smallest odd prime q such that pq+k has exactly j prime factors, where p is the n-th odd prime.
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..1000
EXAMPLE
a(1) = 11 because oddprime(1)*1+2 = 3*11+2 = 35 = 5*7.
a(2) = 11 because oddprime(2)*11+2 = 5*11+2 = 57 = 3*19.
a(3) = 7 because oddprime(3)*7+2 = 7*7+2 = 51 = 3*17.
a(4) = 3 because oddprime(4)*3+2 = 11*3+2 = 35 = 5*7.
a(5) = 5 because oddprime(5)*11+2 = 11*5+2 = 57 = 3*19.
a(6) = 7 because oddprime(6)*7+2 = 13*7+2 = 93 = 3*31.
a(7) = 5 because oddprime(7)*5+2 = 17*5+2 = 87 = 3*29.
a(8) = 13 because oddprime(8)*13+2 = 19*13+2 = 249 = 3*29.
a(9) = 13 because oddprime(9)*13+2 = 23*13+2 = 301 = 7*43.
a(10) = 7 because oddprime(10)*7+2 = 29*5+2 = 205 = 5*41.
MAPLE
isA001358 := proc(n) if numtheory[bigomega](n) = 2 then true ; else false ; fi ; end; A126610 := proc(n) local p, q ; p := ithprime(n+1) ; q := 3 ; while not isA001358(p*q+2) do q := nextprime(q) ; od ; RETURN(q) ; end ; for n from 1 to 100 do printf("%d, ", A126610(n)) ; od : # R. J. Mathar, Feb 10 2007
MATHEMATICA
nn=100; sop[n_]:=Module[{prs=Prime[Range[2, nn+2]], k=1}, While[ PrimeOmega[ prs[[n]] prs[[k]]+2]!=2, k++]; prs[[k]]]; Array[sop, nn] (* Harvey P. Dale, Jan 01 2016 *)
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Jonathan Vos Post, Feb 07 2007
EXTENSIONS
More terms from R. J. Mathar, Feb 10 2007
STATUS
approved