A173631 a(n) = ceiling(sqrt(4*P_n)), where P_n is product of first n primes

2, 3, 5, 11, 29, 97, 347, 1429, 6229, 29873, 160869, 895680, 5448207, 34885543, 228759799, 1568298164, 11417382972, 87698582661, 684947826800, 5606539592683, 47241542317190, 403631914492643, 3587558929043911, 32684217334320604, 308342289648017960, 3036819365023555974

Offset

0,1

Links

Robert Israel, Table of n, a(n) for n = 0..632

Formula

a(n) = ceiling(sqrt(4*A002110(n))). - Michel Marcus, Feb 22 2016

Maple

P:= 1: p:= 1: A[0]:= 2:
for n from 1 to 30 do
  p:= nextprime(p);
  P:= P*p;
  A[n]:= ceil(sqrt(4*P));
od:
seq(A[i], i=0..30); # Robert Israel, Mar 18 2020

Mathematica

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

Prog

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

Crossrefs

Cf. A000040, A002110.

Sequence in context: A265418 A346052 A190197 * A182987 A334814 A364802

Adjacent sequences: A173628 A173629 A173630 * A173632 A173633 A173634

Keyword

nonn

Author

Vladimir Shevelev, Nov 23 2010

Extensions

Extended by T. D. Noe, Nov 23 2010

Status

approved