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A072059
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Smallest prime p such that 2*p+1 has n distinct prime factors.
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2
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2, 7, 97, 577, 7507, 217717, 5232727, 75172597, 1617423307, 59844662377, 2750790860317, 109455887488447, 4621264673452927, 218071376383127767, 10914293640945722527, 662082573402158125717, 41249727342503299116997
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OFFSET
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1,1
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COMMENTS
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Note that for each n=1,...,8, the product of the smallest n-1 distinct prime factors of 2*a(n)+1 is p(n)#/2, where p(n)# is the primorial (A002110) of the n-th prime - and the n-th distinct prime factor >= p(n+1). - Rick L. Shepherd, Jul 06 2002
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LINKS
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EXAMPLE
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a(4)=577=A000040(106): 2*577+1 = 1155 = 11*7*5*3, 4 distinct factors.
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PROG
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(PARI) for (n=1, 8, p=1; until(isprime(p) && omega(2*p+1)==n, p++); print1(p, ", "))
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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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