

A165767


Numbers m such that 2^mm is a semiprime.


4



6, 7, 15, 18, 25, 31, 33, 39, 42, 45, 49, 62, 73, 85, 93, 103, 119, 171, 187, 193, 199, 201, 269, 367, 379, 405, 413, 449, 459, 481, 489, 549, 577, 601, 631, 669, 787, 795, 1399
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OFFSET

1,1


COMMENTS

The largest resp. smallest prime factor of 2^a(n)a(n) is listed in A165768 resp. A165769.
1501, 1587, 1667, 2250, 3393, 5845, 9967, 16147 are terms of this sequence.  Chai Wah Wu, Oct 18 2019


LINKS



FORMULA

a(n)=2k <=> 4^k/2k is prime <=> A165768(n)=2.


EXAMPLE

199 is in this sequence because 2^199199 = 17377902756647509 * 46235097144973199564251065756966919577339221 and these two factors are prime.


MATHEMATICA



PROG

(PARI) for( i=1, 200, bigomega(2^ii)==2 & print1(i", "))


CROSSREFS



KEYWORD

nonn,more,hard


AUTHOR



EXTENSIONS



STATUS

approved



