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Search: id:A137625
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| A137625 |
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First prime in runs where p+4 is semiprime (runs are k=1,2,3,...). |
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+0
4
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| 5, 29, 173, 709, 1741, 8297, 8297, 19213, 175229, 175229
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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Suggested by Carlos Rivera's Puzzle 429 which asks for runs where p+2 is biprime
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FORMULA
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Find a run of primes where p+4 is semiprime
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EXAMPLE
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a(2)=29 because this is the first prime in a run of 2 where p+4 is semiprime (3*11)
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PROGRAM
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UBASIC: 10 'p+4 is biprime 20 N=1 30 A=3:S=sqrt(N) 40 B=N\A: if B*A=N then N=N+2:goto 30 50 A=A+2: if A<=S then 40 60 C=C+1:O=N+4:D=prmdiv(O):E=O\D 70 if E<>prmdiv(E) or E=1 then C=0:goto 90 80 print C; N; D; E; O: if C>=10 then stop 90 N=N+2:goto 30
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CROSSREFS
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Cf. A001358 A137626 A137627 A137628.
Sequence in context: A141814 A122370 A088349 this_sequence A083066 A139174 A081336
Adjacent sequences: A137622 A137623 A137624 this_sequence A137626 A137627 A137628
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KEYWORD
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easy,more,nonn
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AUTHOR
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Enoch Haga (Enokh(AT)comcast.net), Jan 30 2008
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