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

0,1

Links

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

Formula

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

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

Example

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

Mathematica

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

Prog

(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

Crossrefs

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

Sequence in context: A068698 A053300 A322777 * A212729 A218357 A090543

Adjacent sequences: A089278 A089279 A089280 * A089282 A089283 A089284

Keyword

nonn

Author

Reinhard Zumkeller, Oct 30 2003

Extensions

More terms from Ray Chandler, Oct 30 2003

More terms from Ryan Moore, Dec 27 2013

Status

approved