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A272309
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Lesser of two consecutive semiprimes with a prime difference.
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5
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4, 6, 22, 26, 35, 39, 46, 49, 55, 62, 69, 74, 77, 82, 91, 95, 106, 115, 119, 134, 143, 155, 159, 161, 166, 178, 183, 185, 187, 194, 203, 206, 215, 219, 221, 235, 247, 254, 259, 262, 265, 267, 287, 289, 295, 299, 303, 309, 314, 319, 321, 323, 327, 329, 339, 341, 355, 358, 362
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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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39 is in the sequence because 39 = 3*13, the next semiprime is 46 = 2*23, and 46-39 = 7 is prime.
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MATHEMATICA
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L=Select[Range@370, PrimeOmega@# == 2 &]; Pick[Most@L, PrimeQ@ Differences@ L] (* Giovanni Resta, Apr 25 2016 *)
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PROG
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(PARI) proxsem(n)=local(p, s, r); s=0; p=n; while(s==0, p+=1; if(bigomega(p)==2, s=1; r=p)); p
{for(i=1, 400, if(bigomega(i)==2, a=proxsem(i)-i; if(isprime(a), print1(i, ", "))))}
(PARI) list(lim)=my(v=List(), u=v); lim\=1; while(bigomega(lim++)!=2, ); forprime(p=2, lim\2, forprime(q=2, lim\p, listput(v, p*q))); v=Set(v); for(i=1, #v-1, if(isprime(v[i+1]-v[i]), listput(u, v[i]))); Set(u) \\ Charles R Greathouse IV, Apr 29 2016
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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