A128648 a(n) = denominator(Sum_{k=1..n} (-1)^(k+1)/(prime(k)-1)).

1, 2, 4, 12, 60, 5, 80, 720, 7920, 55440, 55440, 6160, 6160, 18480, 425040, 5525520, 160240080, 160240080, 53413360, 53413360, 480720240, 480720240, 19709529840, 19709529840, 39419059680, 197095298400, 3350620072800, 177582863858400

Offset

1,2

Comments

Numbers m such that a(m) equals A128646(m) are listed in A128649.

Links

Table of n, a(n) for n=1..28.

Eric Weisstein's World of Mathematics, Prime Sums

Formula

a(n) = denominator(Sum_{k=1..n} (-1)^(k+1)/(prime(k)-1)).

Mathematica

Table[Denominator[Sum[(-1)^(k+1)*1/(Prime[k]-1), {k, 1, n}]], {n, 1, 36}]

Crossrefs

Cf. A128647 (numerator(Sum_{k=1..n} (-1)^(k+1)/(prime(k)-1))).

Cf. A128646 (denominator(Sum_{k=1..n} 1/(prime(k)-1))).

Cf. A128649, A120271, A119686, A006093, A000040.

Sequence in context: A000568 A177921 A301481 * A128646 A155747 A058254

Adjacent sequences: A128645 A128646 A128647 * A128649 A128650 A128651

Keyword

frac,nonn

Author

Alexander Adamchuk, Mar 18 2007

Status

approved