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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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified July 20 05:56 EDT 2019. Contains 325168 sequences. (Running on oeis4.)