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A100112 If n is the k-th squarefree number then a(n) = k, otherwise a(n) = 0. 11
1, 2, 3, 0, 4, 5, 6, 0, 0, 7, 8, 0, 9, 10, 11, 0, 12, 0, 13, 0, 14, 15, 16, 0, 0, 17, 0, 0, 18, 19, 20, 0, 21, 22, 23, 0, 24, 25, 26, 0, 27, 28, 29, 0, 0, 30, 31, 0, 0, 0, 32, 0, 33, 0, 34, 0, 35, 36, 37, 0, 38, 39, 0, 0, 40, 41, 42, 0, 43, 44, 45, 0, 46, 47, 0, 0, 48, 49, 50, 0, 0, 51, 52, 0 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Eric Weisstein's World of Mathematics, Squarefree

FORMULA

a(A005117(n)) = n;

a(n) = (A013928(n) + 1)*A008966(n).

a(n) = Sum_{k=1..n} mu(lcm(n,k))^2. - Benoit Cloitre, Jun 14 2007

PROG

(PARI) a(n)=sum(k=1, n, moebius(lcm(n, k))^2) \\ Benoit Cloitre, Jun 14 2007

(PARI) first(n)=my(v=vector(n), k); forsquarefree(m=1, n, v[m[1]]=k++); v \\ Charles R Greathouse IV, Jan 08 2018

CROSSREFS

Cf. A005117, A008966, A013928.

Sequence in context: A300816 A007945 A011150 * A198787 A193331 A091246

Adjacent sequences:  A100109 A100110 A100111 * A100113 A100114 A100115

KEYWORD

nonn,easy

AUTHOR

Reinhard Zumkeller, Nov 07 2004

STATUS

approved

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Last modified August 4 20:00 EDT 2020. Contains 336202 sequences. (Running on oeis4.)