A121007 - OEIS

A121007

Denominators of partial alternating sums of Catalan numbers scaled by powers of 1/5.

1, 5, 25, 25, 625, 3125, 15625, 78125, 78125, 1953125, 9765625, 48828125, 244140625, 244140625, 1220703125, 6103515625, 30517578125, 152587890625, 30517578125, 3814697265625, 19073486328125

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OFFSET

0,2

COMMENTS

Numerators are given under A121006. See A121006 for further comments.

LINKS

Table of n, a(n) for n=0..20.

FORMULA

a(n)=denominator(r(n)) with r(n) := rIII(p=1,n) = sum(((-1)^k)*C(k)/5^k,k=0..n) and C(k):=A000108(k) (Catalan). The rationals r(n) are given in lowest terms.

EXAMPLE

Rationals r(n): 1, 4/5, 22/25, 21/25, 539/625, 2653/3125, 13397/15625, 66556/78125, 66842/78125, 1666188/1953125, 8347736/9765625,...

CROSSREFS

The second member (p=2) is A121008/A121009.

Sequence in context: A039936 A124398 A121003 * A043057 A137112 A037410

Adjacent sequences: A121004 A121005 A121006 * A121008 A121009 A121010

KEYWORD

nonn,frac,easy

AUTHOR

Wolfdieter Lang, Aug 16 2006

STATUS

approved