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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.)