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A308970 Smallest prime factor of A001008(n), numerator of n-th harmonic number; a(1) = 1. 5
1, 3, 11, 5, 137, 7, 3, 761, 7129, 11, 97, 13, 29, 1049, 29, 17, 37, 19, 37, 5, 18858053, 3, 761, 5, 109, 34395742267, 521, 29, 43, 31, 109, 2917, 269, 3583, 397, 37, 10839223, 199, 737281, 41, 85691034670497533, 7, 140473, 109, 1553, 47, 911, 7, 23982193, 61, 227, 53, 941, 5953 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Row 1 is taken to be {1} instead of being empty, by convention.

This is the first column of A308968 and A308969, which list the prime factors of A001008.

LINKS

Chai Wah Wu, Table of n, a(n) for n = 1..325

EXAMPLE

   n | A001008(n) written as product of primes

-----+------------------------------------------

   1 | 1 (empty product)

   2 | 3

   3 | 11

   4 | 5 * 5

   5 | 137

   6 | 7 * 7

   7 | 3 * 11 * 11

   8 | 761

   9 | 7129

  10 | 11 * 11 * 61

  11 | 97 * 863

  12 | 13 * 13 * 509

  13 | 29 * 43 * 919

  14 | 1049 * 1117

  15 | 29 * 41233

  16 | 17 * 17 * 8431

  17 | 37 * 1138979

  18 | 19 * 19 * 39541

  19 | 37 * 7440427

  20 | 5 * 11167027

etc., therefore this sequence = 1, 3, 11, 5, 137, 7, 3, 761, ...

PROG

(PARI) row(n)={if(n>1, factor(A001008(n))[1, 1], 1)}

CROSSREFS

Cf. A001008.

Cf. A308967 (number of prime factors), A308968 (table of factorization), A308969 (table of prime divisors), A308971 (greatest prime factor) of A001008(n).

Sequence in context: A114234 A242223 A308969 * A308971 A120299 A341217

Adjacent sequences:  A308967 A308968 A308969 * A308971 A308972 A308973

KEYWORD

nonn

AUTHOR

M. F. Hasler, Jul 03 2019

STATUS

approved

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Last modified April 12 21:13 EDT 2021. Contains 342932 sequences. (Running on oeis4.)