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A069118 Let D(n,s) denotes the denominator of sum(k=1,n,1/k^s); sequence gives values of n such that D(n,4)/D(n,2) is a perfect square. 1
1, 2, 3, 4, 5, 6, 7, 8, 9, 15, 16, 17, 18, 19, 28, 29, 30, 31, 32, 33, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Robert Israel, Table of n, a(n) for n = 1..3952

EXAMPLE

3 is in the sequence because 1/1^4 +1/2^4 + 1/3^4 = 1393/1296 and 1/1^2 + 1/2^2 + 1/3^2 = 49/36, and 1296/36 = 36 = 6^2.

MAPLE

dd:= (n, s) -> denom(add(1/k^s, k=1..n)):

select(t -> issqr(dd(t, 4)/dd(t, 2)), [$1..1000]); # Robert Israel, May 18 2014

PROG

(PARI) default(realprecision, 1000); for(n=1, 300, if(sqrt(denominator(sum(i=1, n, 1/i^4))/denominator(sum(i=1, n, 1/i^2))) == floor(sqrt(denominator(sum(i=1, n, 1/i^4))/denominator(sum(i=1, n, 1/i^2)))), print1(n, ", ")))

CROSSREFS

Sequence in context: A073526 A032992 A190298 * A328933 A032978 A197181

Adjacent sequences:  A069115 A069116 A069117 * A069119 A069120 A069121

KEYWORD

easy,nonn

AUTHOR

Benoit Cloitre, Apr 07 2002

STATUS

approved

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Last modified October 15 21:38 EDT 2021. Contains 348034 sequences. (Running on oeis4.)