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A265675 Number of smaller squarefree numbers that are coprime to the n-th squarefree number. 4
0, 1, 2, 3, 2, 5, 3, 7, 8, 5, 6, 11, 12, 8, 9, 15, 10, 17, 8, 19, 13, 13, 15, 23, 15, 17, 26, 11, 28, 18, 30, 21, 32, 25, 23, 23, 36, 37, 25, 30, 18, 41, 29, 22, 44, 45, 30, 36, 22, 49, 32, 51, 41, 34, 39, 55, 44, 41, 38, 47, 60, 61, 30, 63, 36, 43, 66, 67 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

a(n) = number of A005117(k) such that A005117(k) and A005117(n) are coprime, k = 1..n-1.

LINKS

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

FORMULA

a(n) = Sum_{k=1..n-1} A008966(A005117(n)*A005117(k)).

EXAMPLE

A005117(7) = 10, A005117(1..6) = [1,2,3,5,6,7],

->  a(7) = #{1,3,7} = 3;

A005117(8) = 11, A005117(1..7) = [1,2,3,5,6,7,10],

->  a(8) = #{1,2,3,5,6,7,10} = 7;

A005117(9) = 13, A005117(1..8) = [1,2,3,5,6,7,10,11],

->  a(9) = #{1,2,3,5,6,7,10,11} = 8;

A005117(10) = 14, A005117(1..9) = [1,2,3,5,6,7,10,11,13],

->  a(10) = #{1,3,5,11,13} = 5;

A005117(11) = 15, A005117(1..10) = [1,2,3,5,6,7,10,11,13,14],

->  a(11) = #{1,2,7,11,13,14} = 6.

PROG

(Haskell)

import Data.List (inits)

a265675 n = a265675_list !! (n-1)

a265675_list = map (\(x:xs) -> length $ filter ((== 1) . gcd x) xs) $

                   map reverse $ tail $ inits a005117_list

CROSSREFS

Cf. A005117, A008966.

Sequence in context: A335285 A336268 A075105 * A094020 A165609 A141465

Adjacent sequences:  A265672 A265673 A265674 * A265676 A265677 A265678

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Dec 13 2015

STATUS

approved

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Last modified April 13 10:24 EDT 2021. Contains 342935 sequences. (Running on oeis4.)