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A082020 Decimal expansion of 15/Pi^2. 16
1, 5, 1, 9, 8, 1, 7, 7, 5, 4, 6, 3, 5, 0, 6, 6, 5, 7, 1, 6, 5, 8, 1, 9, 1, 9, 4, 8, 1, 4, 5, 9, 1, 4, 5, 8, 3, 5, 6, 5, 3, 8, 1, 6, 2, 0, 0, 8, 3, 6, 9, 8, 2, 3, 2, 6, 8, 4, 1, 3, 5, 4, 7, 8, 4, 1, 2, 5, 9, 6, 8, 1, 4, 4, 3, 3, 5, 3, 1, 6, 1, 7, 8, 6, 8, 1, 3, 9, 1, 0, 8, 8, 8, 4, 3, 2, 7, 5, 6 (list; constant; graph; refs; listen; history; text; internal format)
OFFSET

1,2

REFERENCES

W Hürlimann, Dedekind's arithmetic function and primitive four squares counting functions, Journal of Algebra, Number Theory: Advances and Applications, Volume 14, Number 2, 2015, Pages 73-88; http://scientificadvances.co.in; DOI: http://dx.doi.org/10.18642/jantaa_7100121599

LINKS

Table of n, a(n) for n=1..99.

S. Ramanujan, Irregular numbers, J. Indian Math. Soc. 5 (1913) 105-106.

Eric Weisstein's World of Mathematics, Prime Sums

Eric Weisstein's World of Mathematics, Moebius Function

Eric Weisstein's World of Mathematics, Prime Products

FORMULA

Product_{n >= 1} (1+1/prime(n)^2) = 15/Pi^2. - Ramanujan

Equals Zeta(2)/Zeta(4)=A013661/A013662 = sum_{n>=1} mu(n)^2/n^2 = sum_{n>=1} |mu(n)|/n^2 . - Enrique Pérez Herrero, Jan 15 2012

Equals sum{n>=1} 1/A005117(n)^2 .- Enrique Pérez Herrero, Mar 30 2012

EXAMPLE

1.51981775463506657...

MATHEMATICA

A082020[digits_] := First[RealDigits[Zeta[2]/Zeta[4], 10, digits]]; A082020[100] (* Enrique Pérez Herrero, Jan 15 2012 *)

CROSSREFS

Cf. A157290

Sequence in context: A154605 A114594 A021662 * A256559 A182498 A147406

Adjacent sequences:  A082017 A082018 A082019 * A082021 A082022 A082023

KEYWORD

nonn,cons

AUTHOR

N. J. A. Sloane, May 09 2003

STATUS

approved

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Last modified June 27 11:25 EDT 2017. Contains 288788 sequences.