OFFSET
1,1
COMMENTS
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..4377 (terms below 10^60)
EXAMPLE
a(1) = (2^0)*(3^1) + 1 = (2^2)*(3^0) - 1 = 4 = 2*2, a semiprime.
a(2) = (2^3)*(3^0) + 1 = 9 = 3*3.
a(3) = (2^0)*(3^2) + 1 = 10 = 2*5.
a(4) = (2^4)*(3^0) - 1 = 15 = 3*5.
MATHEMATICA
mx = 4000; A003586 = Flatten@ Table[2^i*3^j, {i, 0, Log[2, mx]}, {j, 0, Log[3, mx/2^i]}]; Union@ Join[ Select[A003586, PrimeOmega[# - 1] == 2 &] - 1, Select[A003586, PrimeOmega[# - 1] == 2 || PrimeOmega[# + 1] == 2 &] + 1] (* Robert G. Wilson v, Nov 22 2012 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Jonathan Vos Post, Nov 22 2012
STATUS
approved