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A175682
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Maximal run length of positive primes of the form ..., n-2*3*5, n-2*3, n-2, n, n+2, n+2*3, n+2*3*5, ...
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3
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0, 1, 2, 0, 4, 0, 2, 0, 0, 0, 4, 0, 3, 0, 0, 0, 5, 0, 3, 0, 0, 0, 1, 0, 0, 0, 0, 0, 2, 0, 2, 0, 0, 0, 0, 0, 1, 0, 0, 0, 9, 0, 4, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 2, 0, 2, 0, 0, 0, 0, 0, 1, 0, 0, 0, 2, 0, 4, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 6, 0, 4, 0, 0
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OFFSET
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1,3
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LINKS
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FORMULA
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EXAMPLE
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MATHEMATICA
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Array[If[PrimeQ@ #, Block[{s = {1}, t = {1}}, While[PrimeQ[# + Times @@ Prime@ s], AppendTo[s, s[[-1]] + 1]]; While[And[# > 0, PrimeQ[#]] &[# - Times @@ Prime@ t], AppendTo[t, t[[-1]] + 1]]; Last[s] + Last[t] - 1], 0] &, 105] (* Michael De Vlieger, Jan 03 2019 *)
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PROG
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(PARI) A175682(n) = if(!isprime(n), 0, my(pr=2, dn=1, dp=1, rl=1); for(k=1, oo, if(!isprime(n-pr), dn=0); if(!isprime(n+pr), dp=0); if(!(dn+dp), return(rl)); rl += (dn+dp); pr *= prime(1+k))); \\ (Note that isprime in PARI/GP 2.9.4 returns 0 on all negative arguments) - Antti Karttunen, Jan 03 2019
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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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