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A131867
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a(n) is the 2^n-th semiprime.
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1
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4, 6, 10, 22, 46, 93, 202, 407, 849, 1774, 3693, 7671, 15999, 33146, 68703, 142682, 295003, 610757, 1261573, 2603453, 5369633, 11058907, 22758881, 46796443, 96132103, 197329777, 404737537, 829538129, 1698995201, 3477431507, 7113030933, 14540737711
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OFFSET
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0,1
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COMMENTS
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The PARI code allows one to resume at the k-th semiprime, e.g., SP(295003,65536) and to change the output interval, e.g., SP(_,_,10) = A114125, SP(_,_,-1) = A001358.
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LINKS
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FORMULA
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EXAMPLE
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a(0)=4 is the first semiprime;
a(1)=6 is the 2nd semiprime;
a(16)=295003 is the 65536th semiprime.
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PROG
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(PARI) SP( n=0 /*tested number*/, c=0 /*count of semiprimes*/, step=2)={ local( l=c+!c ); /* negative/positive step means arithmetic/geometric progression of output threshold l */ until( 0, until(l<=c++, until(bigomega(n+=1)==2, )); print1(/*c ":" */ n ", "); if(step>0, l*=step, l-=step))}
(Perl) use ntheory ":all"; my($i, $g)=(0, 0); forsemiprimes { print $g++, " $_\n" if ++$i == 1<<$g; } 10**8; # Dana Jacobsen, Sep 10 2018
(Perl) use ntheory ":all"; print "$_ ", nth_semiprime(1<<$_), "\n" for 0..40; # Dana Jacobsen, Oct 08 2018
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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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