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A110606
Numbers n whose base 8 representations, interpreted as base 10 integers, are semiprimes.
6
4, 6, 8, 12, 13, 17, 18, 21, 22, 27, 28, 29, 38, 41, 45, 47, 50, 53, 60, 63, 70, 73, 77, 81, 82, 83, 91, 92, 97, 98, 99, 101, 102, 109, 113, 118, 127, 129, 130, 131, 133, 134, 139, 140, 141, 143, 145, 150, 157, 159, 167, 171, 172, 178, 181, 183, 188, 193, 194, 195
OFFSET
1,1
COMMENTS
A108873 is the equivalent using base 3. A110602 is the equivalent using base 4. A110603 is the equivalent using base 5. A110604 is the equivalent using base 6. A110605 is the equivalent using base 7. A110607 is the equivalent using base 9.
EXAMPLE
a(1) = 4 because 4 (base 8) = 4 (base 10) = 2 * 2, a semiprime (A001358).
a(2) = 6 because 6 (base 8) = 6 (base 10) = 2 * 3.
a(3) = 8 because 8 (base 8) = 10 and 10 (base 10) = 2 * 5.
a(4) = 12 because 12 (base 8) = 14 and 14 (base 10) = 2 * 7.
a(5) = 13 because 13 (base 8) = 15 and 15 (base 10) = 3 * 5.
MATHEMATICA
Select[Range[195], Plus @@ Last /@ FactorInteger[FromDigits[IntegerDigits[ #, 8]]] == 2 &] (* Ray Chandler, Aug 05 2005 *)
KEYWORD
base,easy,nonn
AUTHOR
Jonathan Vos Post, Jul 30 2005
EXTENSIONS
Extended by Ray Chandler, Aug 05 2005
STATUS
approved