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A272307
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Lesser of two consecutive semiprimes whose difference is also semiprime.
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5
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10, 15, 51, 58, 65, 87, 111, 123, 129, 146, 209, 226, 237, 249, 274, 278, 291, 305, 335, 346, 365, 371, 377, 382, 403, 407, 427, 447, 454, 485, 489, 493, 497, 505, 529, 538, 545, 573, 591, 597, 629, 635, 649, 681, 699, 707, 713, 749, 767, 781, 785, 803, 807, 831, 843, 889, 901
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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1,1
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LINKS
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Harvey P. Dale, Table of n, a(n) for n = 1..2000
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EXAMPLE
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65 is in the sequence because 65 = 5*13, the next semiprime is 69 = 3*23, and 69-65 = 4 = 2*2, is also semiprime.
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MATHEMATICA
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s[n_] := PrimeOmega@n==2; L=Select[Range@910, s]; Pick[ Most@L, s /@ Differences@ L] (* Giovanni Resta, Apr 25 2016 *)
Select[Partition[Select[Range[1000], PrimeOmega[#]==2&], 2, 1], PrimeOmega[#[[2]]-#[[1]]]==2&][[All, 1]] (* Harvey P. Dale, Oct 13 2022 *)
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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, 1000, if(bigomega(i)==2, a=proxsem(i); if(bigomega(a-i)==2, print1(i, ", "))))}
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CROSSREFS
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Cf. A001358, A272306, A272308, A272309.
Sequence in context: A048061 A188651 A330203 * A092192 A119039 A047189
Adjacent sequences: A272304 A272305 A272306 * A272308 A272309 A272310
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KEYWORD
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nonn
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AUTHOR
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Antonio Roldán, Apr 25 2016
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STATUS
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approved
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