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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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3
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OFFSET
| 1,1
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COMMENTS
| Suggested by Carlos Rivera's Puzzle 429 which asks for runs where p+2 is biprime
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FORMULA
| Find a run of primes where p+4 is semiprime
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EXAMPLE
| 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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PROG
| 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
| Cf. A001358 A137626 A137627 A137628.
Sequence in context: A175883 A122370 A088349 * A083066 A163611 A160906
Adjacent sequences: A137622 A137623 A137624 * A137626 A137627 A137628
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KEYWORD
| more,nonn
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AUTHOR
| Enoch Haga (Enokh(AT)comcast.net), Jan 30 2008
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