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%I #8 Oct 19 2017 03:14:03
%S 2,7,97,577,7507,217717,5232727,75172597,1617423307,59844662377,
%T 2750790860317,109455887488447,4621264673452927,218071376383127767,
%U 10914293640945722527,662082573402158125717,41249727342503299116997
%N Smallest prime p such that 2*p+1 has n distinct prime factors.
%C 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
%e a(4)=577=A000040(106): 2*577+1 = 1155 = 11*7*5*3, 4 distinct factors.
%o (PARI) for (n=1,8, p=1; until(isprime(p) && omega(2*p+1)==n, p++); print1(p,","))
%Y Cf. A001221, A023589, A072055, A072060.
%K nonn
%O 1,1
%A _Reinhard Zumkeller_, Jun 11 2002
%E More terms from _Rick L. Shepherd_, Jul 06 2002
%E More terms from _Don Reble_, Apr 15 2003
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