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A125504 Smallest number k such that the numerator of alternating generalized harmonic number H'(k,n) = Sum[ (-1)^(i+1) * 1/i^n, {i,1,k} ] is a prime. 0
3, 2, 2, 3, 2, 19, 2, 146, 87, 3, 16, 3, 2, 249, 15, 87, 2, 699, 2 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

a(n) = 2 for n in A000043.

a(n) = 3 for n in {1,4,10,12,24,27,39,...}.

a(n) = 5 for n in {26,76,132,205,238,...}.

a(n) = 9 for n in {100,200,...}.

a(n) = 15 for n in {15,33,65,...}.

a(21) = 18. a(22) = 13. a(41) = 6. a(72) = 11. a(173) = 8.

a(20) > 2100 [From Max Alekseyev, Jul 07 2009]

LINKS

Table of n, a(n) for n=1..19.

Eric Weisstein, Link to a section of The World of Mathematics. Harmonic Number.

CROSSREFS

Cf. A058313, A119682, A120296, A001008, A000043.

Sequence in context: A049234 A299351 A294299 * A243929 A075392 A069901

Adjacent sequences:  A125501 A125502 A125503 * A125505 A125506 A125507

KEYWORD

hard,more,nonn

AUTHOR

Alexander Adamchuk, Dec 28 2006, Jan 31 2007

EXTENSIONS

More terms from Max Alekseyev, Jul 07 2009

STATUS

approved

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Last modified February 21 07:18 EST 2018. Contains 299390 sequences. (Running on oeis4.)