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A282132 Imaginary part of n!*Sum_{k=1..n} i^(k-1)/k, where i is sqrt(-1). 3
0, 1, 3, 6, 30, 300, 2100, 11760, 105840, 1421280, 15634080, 147692160, 1919998080, 33106993920, 496604908800, 6638004172800, 112846070937600, 2386916704972800, 45351417394483200, 785383247480832000, 16493048197097472000, 413938002507853824000 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

LINKS

Daniel Suteu, Table of n, a(n) for n = 1..100

FORMULA

a(n) ~ log(sqrt(2)) * n!.

a(1) = 0, a(n+1) = a(n)*(n+1) + n!*sin(Pi*n/2).

EXAMPLE

For n=5, a(5) = 30, which is the imaginary part of 5!*(1/1 + i/2 - 1/3 - i/4 + 1/5) = 104+30*i.

PROG

(PARI) a(n) = imag(n!*sum(k=1, n, I^(k-1)/k));

CROSSREFS

The corresponding real part is A281964.

Cf. A016655, A024167.

Sequence in context: A088506 A061137 A012280 * A002164 A117805 A154135

Adjacent sequences:  A282129 A282130 A282131 * A282133 A282134 A282135

KEYWORD

nonn

AUTHOR

Daniel Suteu, Feb 06 2017

STATUS

approved

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Last modified October 22 10:55 EDT 2018. Contains 316436 sequences. (Running on oeis4.)