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A131867
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2^n-th semiprime.
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0
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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, 29707839373, 60662588879
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,1
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COMMENTS
| 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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FORMULA
| a(n)=A001358(2^n)
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EXAMPLE
| a(0)=4 is the first semiprime, a(1)=6 is the 2nd semiprime ; a(16)=295003 is the 65536-th semiprime.
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PROG
| (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))}
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CROSSREFS
| Cf. A001358 (semiprimes), A114125.
Sequence in context: A096817 A185913 A077065 * A032392 A136838 A109378
Adjacent sequences: A131864 A131865 A131866 * A131868 A131869 A131870
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KEYWORD
| nonn
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AUTHOR
| M. F. Hasler (Maximilian.Hasler(AT)gmail.com), Oct 04 2007
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EXTENSIONS
| a(23)-a(28) from Donovan Johnson (donovan.johnson(AT)yahoo.com), Nov 11 2008
a(29)-a(33) from Max Alekseyev (maxale(AT)gmail.com), May 07 2010
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