This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A072059 #8 Oct 19 2017 03:14:03 %S A072059 2,7,97,577,7507,217717,5232727,75172597,1617423307,59844662377, %T A072059 2750790860317,109455887488447,4621264673452927,218071376383127767, %U A072059 10914293640945722527,662082573402158125717,41249727342503299116997 %N A072059 Smallest prime p such that 2*p+1 has n distinct prime factors. %C A072059 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 A072059 a(4)=577=A000040(106): 2*577+1 = 1155 = 11*7*5*3, 4 distinct factors. %o A072059 (PARI) for (n=1,8, p=1; until(isprime(p) && omega(2*p+1)==n, p++); print1(p,",")) %Y A072059 Cf. A001221, A023589, A072055, A072060. %K A072059 nonn %O A072059 1,1 %A A072059 _Reinhard Zumkeller_, Jun 11 2002 %E A072059 More terms from _Rick L. Shepherd_, Jul 06 2002 %E A072059 More terms from _Don Reble_, Apr 15 2003