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A225801
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The only semiprime s such that 2*a < s < 2*b where a, b are consecutive semiprimes.
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1
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51, 69, 74, 77, 106, 111, 115, 129, 187, 226, 235, 237, 267, 291, 314, 355, 371, 403, 407, 411, 422, 427, 437, 497, 519, 533, 591, 597, 649, 655, 669, 713, 723, 763, 785, 789, 831, 893, 905, 939, 943, 965, 1003, 1027, 1037, 1059, 1067, 1073, 1126, 1159, 1165
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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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74 is the only semiprime in the interval [2*35, 2*38} = [70, 76] where 35, 38 are consecutive semiprimes.
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PROG
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(PARI) issemi(n)=bigomega(n)==2
precsemi(n)=while(!issemi(n--), ); n
nextsemi(n)=while(!issemi(n++), ); n
is(n)=if(!issemi(n), return(0)); my(a=precsemi(ceil(n/2)), b=nextsemi(n\2)); nextsemi(a)==b && nextsemi(2*a)==n && precsemi(2*b)==n \\ Charles R Greathouse IV, Mar 18 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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STATUS
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approved
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