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 A308969 Table, read by rows: row n contains the prime divisors of A001008 (numerator of n-th harmonic number), without repetitions. 4
 1, 3, 11, 5, 137, 7, 3, 11, 761, 7129, 11, 61, 97, 863, 13, 509, 29, 43, 919, 1049, 1117, 29, 41233, 17, 8431, 37, 1138979, 19, 39541, 37, 7440427, 5, 11167027, 18858053, 3, 23, 53, 227, 761, 583859, 5, 577, 467183, 109, 312408463 (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. LINKS EXAMPLE n | A001008(n) written as product of primes -----+---------------------------------------------    1 | 1 (empty product)    2 | 3    3 | 11    4 | 5 * 5   (So 5 is the only prime divisor, and row(4) = {5}.)    5 | 137    6 | 7 * 7    7 | 3 * 11 * 11       whence row(7) = {3, 11}.)    8 | 761    9 | 7129   10 | 11 * 11 * 61      whence row(10) = {11, 61}.   11 | 97 * 863   12 | 13 * 13 * 509     whence row(16) = {13, 509}.   13 | 29 * 43 * 919     whence row(13) = {29, 43, 919}.   14 | 1049 * 1117   15 | 29 * 41233   16 | 17 * 17 * 8431    whence row(16) = {17, 8431}.   17 | 37 * 1138979   18 | 19 * 19 * 39541   whence row(18) = {19, 39541}.   19 | 37 * 7440427   20 | 5 * 11167027 etc. MATHEMATICA Table[FactorInteger[Numerator[HarmonicNumber[n]]][[All, 1]], {n, 30}]// Flatten (* Harvey P. Dale, Sep 14 2020 *) PROG (PARI) row(n)={if(n>1, factor(A001008(n))[, 1]~, [1])} CROSSREFS Cf. A001008. Cf. A308967 (number of prime factors), A308968 (table of factorization), A308970 & A308971 (smallest & greatest prime factor) of A001008(n). Sequence in context: A212402 A114234 A242223 * A308970 A308971 A120299 Adjacent sequences:  A308966 A308967 A308968 * A308970 A308971 A308972 KEYWORD nonn,tabf AUTHOR M. F. Hasler, Jul 03 2019 STATUS approved

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Last modified April 17 23:03 EDT 2021. Contains 343071 sequences. (Running on oeis4.)