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A239038
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Semiprimes of the form (2^k - m)*(m*2^k - 1).
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2
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9, 14, 49, 55, 94, 115, 446, 611, 869, 961, 4031, 4315, 7891, 7934, 8143, 11651, 16129, 16255, 32254, 37301, 51089, 54701, 60311, 64931, 65279, 65441, 241519, 287509, 321029, 367459, 384799, 446201, 495409, 513847, 521029, 808691, 1297915, 1582619, 1685219, 1883681
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OFFSET
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1,1
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LINKS
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EXAMPLE
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9 is in this sequence because (2^1-1)*(1*2^1-1) = 3*3 = 9 is semiprime for k=1 and m=1,
49 is in this sequence because (2^3-1)*(1*2^3-1) = 7*7 = 49 is semiprime for k=3 and m=1,
115 is in this sequence because (2^3-3)*(3*2^3-1) = 5*23 = 115 is semiprime for k=3 and m=3.
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PROG
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(PARI) list(lim)=my(v=List(), t); for(k=1, log(sqrt(lim)+2)\log(2), for(m=1, min((lim+1)>>k, 2^k-2), my(a=2^k-m, b=m<<k-1, n=a*b); if(n<=lim && isprime(a) && isprime(b), listput(v, n))); t=4^k-2^k-1; if(t<=lim && bigomega(t)==2, listput(v, t))); Set(v) \\ Charles R Greathouse IV, Mar 11 2014
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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