A089281 - OEIS

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

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OFFSET

0,1

LINKS

Ryan Moore, Table of n, a(n) for n = 0..100 (first 60 terms from Ray Chandler)

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 fector), A011545 (numbers made from inital 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