

A137625


The initial prime in the first set of n consecutive primes for which p+4 is semiprime.


3



2, 29, 173, 709, 1741, 8297, 8297, 19213, 175229, 175229, 33952609, 4377722623, 4377722623, 1242030992173, 1242030992173
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OFFSET

1,1


COMMENTS

Suggested by Carlos Rivera's Puzzle 429 which asks for runs where p+2 is biprime.


LINKS



EXAMPLE

a(2)=29 because this is the first prime in a run of 2 where p+4 is semiprime (3*11).


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


CROSSREFS



KEYWORD

more,nonn


AUTHOR



EXTENSIONS



STATUS

approved



