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 A101236 #11 Mar 30 2015 12:57:24 %S A101236 1,1,3,45,45,15855,280665,4774980,4393585185,6522452145,166260770280, %T A101236 4321816939440,15939674132892510,22654052989616460555, %U A101236 22654052989616460555,202608454566431632290 %N A101236 Smallest i such that i*2^(2)-1, ..., i*2^(n+2)-1 are primes. %C A101236 (2^2)*3-1=11, (2^3)*3-1=23 and (2^4)*3-1=47 are primes so 3 is the third entry. %C A101236 For every x in A001122, the x-th term of this sequence and every succeeding term is divisible by x. For example 3 divides the 3rd and every succeeding term, 5 divides the 5th and every succeeding term. %C A101236 The sequences of primes generated by these numbers are a type of Cunningham chain of the first kind (CC1). Since the longest known CC1 chain is of length 16, the next terms are currently unknown. - Douglas Stones (dssto1(AT)student.monash.edu.au), Mar 16 2005 %H A101236 Paul Jobling, <a href="http://www.utm.edu/research/primes/programs/NewPGen/">NewPGen</a> %H A101236 G. Loeh, <a href="http://dx.doi.org/10.1090/S0025-5718-1989-0979939-8">Long chains of nearly doubled primes</a>, Mathematics of Computation, Vol. 53, No. 188, Oct 1989, pp. 751-759. %Y A101236 Cf. A002515, A101790, A101794. %K A101236 hard,nonn %O A101236 0,3 %A A101236 Douglas Stones (dssto1(AT)student.monash.edu.au), Dec 16 2004; revised Dec 31 2004 %E A101236 More terms from Douglas Stones (dssto1(AT)student.monash.edu.au), Mar 16 2005