A089281 Smallest prime factor of floor(Pi*10^n).

3, 31, 2, 3, 5, 314159, 2, 2, 3, 3, 5, 2, 13, 163, 43, 13, 2, 317213509, 2, 2, 2, 2, 2, 2, 83, 41, 2, 3, 2, 3, 3, 5, 2, 2, 2, 2, 2, 31415926535897932384626433832795028841, 13, 59, 3, 2, 3, 3, 3, 3, 3, 31, 3, 1657, 2, 3, 2, 2, 2, 29, 13, 2, 3, 2

Offset: 0

Author

Reinhard Zumkeller, Oct 30 2003

Keywords

• nonn

Examples

			n = 10: floor(Pi*10^10) = 31415926535 = 5*7*31*28954771: a(10) = 5.
		

Links

• Tyler Busby, Table of n, a(n) for n = 0..572 (terms 0..59 from Ray Chandler, terms 60..100 from Ryan Moore)

Crossrefs

Cf. A078604, A000796 (decimals of Pi), A020639 (smallest prime fector), A011545 (numbers made from inital digits of Pi), A060421 (1 + indices of primes in this sequence).

Programs

Mathematica

a[n_] := FactorInteger[IntegerPart[Pi*10^n]][[1, 1]];
Table[a[n], {n, 0, 59}]  (* Peter Luschny, Mar 15 2024 *)

PARI

a(n) = factor(floor(Pi*10^n))[1, 1]; \\ Michel Marcus, Dec 28 2013

PARI

A089281(n)={localprec(n+3); factor(Pi\10^-n)[1, 1]} \\ M. F. Hasler, Mar 15 2024

Formula

a(n) = A020639(A011545(n)).

a(n) is prime (<=> in A000040) iff n+1 is in A060421. - M. F. Hasler, Mar 15 2024

Extensions

More terms from Ray Chandler, Oct 30 2003

More terms from Ryan Moore, Dec 27 2013