A173631 - OEIS

%I #26 Jun 16 2022 10:24:59

%S 2,3,5,11,29,97,347,1429,6229,29873,160869,895680,5448207,34885543,

%T 228759799,1568298164,11417382972,87698582661,684947826800,

%U 5606539592683,47241542317190,403631914492643,3587558929043911,32684217334320604,308342289648017960,3036819365023555974

%N a(n) = ceiling(sqrt(4*P_n)), where P_n is product of first n primes

%H Robert Israel, <a href="/A173631/b173631.txt">Table of n, a(n) for n = 0..632</a>

%F a(n) = ceiling(sqrt(4*A002110(n))). - _Michel Marcus_, Feb 22 2016

%p P:= 1: p:= 1: A[0]:= 2:

%p for n from 1 to 30 do

%p   p:= nextprime(p);

%p   P:= P*p;

%p   A[n]:= ceil(sqrt(4*P));

%p od:

%p seq(A[i],i=0..30); # _Robert Israel_, Mar 18 2020

%t p=4; Join[{Sqrt[p]}, Table[p=p*Prime[n]; Ceiling[Sqrt[p]], {n, 25}]]

%o (PARI) a(n) = sqrtint(4*prod(k=1, n, prime(k)) - 1) + 1; \\ _Michel Marcus_, Feb 22 2016; corrected Jun 16 2022

%Y Cf. A000040, A002110.

%K nonn

%O 0,1

%A _Vladimir Shevelev_, Nov 23 2010

%E Extended by _T. D. Noe_, Nov 23 2010