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 A089281 Smallest prime factor of floor(Pi*10^n). 5
 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 (list; graph; refs; listen; history; text; internal format)
 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

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Last modified August 13 14:18 EDT 2024. Contains 375142 sequences. (Running on oeis4.)