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A279052
Semiprimes whose binary and ternary representations are prime when read in decimal.
1
295, 1189, 2515, 4399, 4897, 5137, 7045, 7261, 7999, 8065, 9019, 9637, 10579, 10951, 10963, 11035, 11233, 12679, 13315, 13603, 13849, 16279, 18295, 20065, 20467, 20497, 23089, 23419, 23551, 23983, 26359, 27007, 27301, 27787, 29647, 33127, 33253, 33763, 34189, 34411
OFFSET
1,1
LINKS
K. D. Bajpai and Charles R Greathouse IV, Table of n, a(n) for n = 1..10000 (first 4075 terms from K. D. Bajpai)
EXAMPLE
295 is in the sequence because 295 = 5*59 (semiprime), 295_10 = 100100111_2 = 101221_3, and both 100100111_10 and 101221_10 are prime.
1189 is in the sequence because 1189 = 29*41 (semiprime), and both its binary representation 10010100101 and its ternary representation 1122001, if read as decimal numbers, are prime.
MATHEMATICA
Select[Range[50000], PrimeOmega[#] == 2 && PrimeQ[FromDigits[IntegerDigits[#, 2]]] && PrimeQ[FromDigits[IntegerDigits[#, 3]]] &]
PROG
(PARI) has(n, b)=isprime(fromdigits(digits(n, b), 10))
list(lim)=my(v=List(), t); forprime(p=2, lim\2, forprime(q=2, min(lim\p, p), if(has(t=p*q, 2) && has(t, 3), listput(v, t)))); Set(v) \\ Charles R Greathouse IV, Dec 05 2016
CROSSREFS
Subsequence of A001358.
Sequence in context: A074868 A277338 A252083 * A237803 A238512 A003780
KEYWORD
nonn,base
AUTHOR
K. D. Bajpai, Dec 05 2016
STATUS
approved