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 A173631 #28 Jul 22 2025 07:50:53
%S A173631 2,3,5,11,29,97,347,1429,6229,29873,160869,895680,5448207,34885543,
%T A173631 228759799,1568298164,11417382972,87698582661,684947826800,
%U A173631 5606539592683,47241542317190,403631914492643,3587558929043911,32684217334320604,308342289648017960,3036819365023555974
%N A173631 a(n) = ceiling(sqrt(4*P_n)), where P_n is product of first n primes.
%H A173631 Robert Israel, <a href="/A173631/b173631.txt">Table of n, a(n) for n = 0..632</a>
%F A173631 a(n) = ceiling(sqrt(4*A002110(n))). - _Michel Marcus_, Feb 22 2016
%p A173631 P:= 1: p:= 1: A[0]:= 2:
%p A173631 for n from 1 to 30 do
%p A173631 p:= nextprime(p);
%p A173631 P:= P*p;
%p A173631 A[n]:= ceil(sqrt(4*P));
%p A173631 od:
%p A173631 seq(A[i],i=0..30); # _Robert Israel_, Mar 18 2020
%t A173631 p=4; Join[{Sqrt[p]}, Table[p=p*Prime[n]; Ceiling[Sqrt[p]], {n, 25}]]
%o A173631 (PARI) a(n) = sqrtint(4*prod(k=1, n, prime(k)) - 1) + 1; \\ _Michel Marcus_, Feb 22 2016; corrected Jun 16 2022
%Y A173631 Cf. A000040, A002110.
%K A173631 nonn
%O A173631 0,1
%A A173631 _Vladimir Shevelev_, Nov 23 2010
%E A173631 Extended by _T. D. Noe_, Nov 23 2010