

A110607


Numbers n whose base 9 representations, interpreted as base 10 integers, are semiprimes.


7



4, 6, 9, 13, 14, 19, 20, 23, 24, 30, 31, 32, 35, 42, 46, 50, 52, 53, 56, 59, 67, 70, 74, 77, 78, 79, 87, 91, 95, 98, 100, 101, 102, 111, 112, 118, 119, 120, 122, 123, 131, 134, 136, 141, 151, 152, 156, 158, 160, 163, 164, 165, 167, 168, 174, 175, 176, 178, 179, 181
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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. A110606 is the equivalent using base 8.


LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..1000


EXAMPLE

a(1) = 4 because 4 (base 9) = 4 (base 10) = 2 * 2, a semiprime (A001358).
a(2) = 6 because 6 (base 9) = 6 (base 10) = 2 * 3.
a(3) = 9 because 9 (base 9) = 10 and 10 (base 10) = 2 * 5.
a(4) = 13 because 13 (base 9) = 14 and 14 (base 10) = 2 * 7.
a(5) = 14 because 14 (base 9) = 15 and 15 (base 10) = 3 * 5.


MATHEMATICA

Select[Range[181], Plus @@ Last /@ FactorInteger[FromDigits[IntegerDigits[ #, 9]]] == 2 &] (*Chandler*)
Select[Range[200], PrimeOmega[FromDigits[IntegerDigits[#, 9]]]==2&] (* Harvey P. Dale, Dec 02 2018 *)


CROSSREFS

Cf. A001358, A007095, A108873, A110602, A110603, A110604, A110605, A110607.
Sequence in context: A078782 A165897 A020165 * A085802 A084916 A187910
Adjacent sequences: A110604 A110605 A110606 * A110608 A110609 A110610


KEYWORD

base,easy,nonn


AUTHOR

Jonathan Vos Post, Jul 30 2005


EXTENSIONS

Extended by Ray Chandler, Aug 05 2005


STATUS

approved



