The On-Line Encyclopedia of Integer Sequences (OEIS)

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A048983

As n runs through composite numbers, a(n) = number of composite d < n such that gcd(d,n) = 1.
(history; published version)

#8 by Jon E. Schoenfield at Fri Oct 25 21:20:26 EDT 2019

STATUS

editing

approved

#7 by Jon E. Schoenfield at Fri Oct 25 21:20:19 EDT 2019

NAME

As n runs through composite numbers, a(n) = number of composite d < n such that GCDgcd(d,n) = 1.

EXAMPLE

9 is 4th composite number, GCDgcd(9,4) =GCD gcd(9,8) = 1, so a(4) = 2.

STATUS

approved

editing

#6 by Joerg Arndt at Sun Jul 14 04:37:21 EDT 2013

STATUS

proposed

approved

#5 by Michel Marcus at Sun Jul 14 04:15:51 EDT 2013

STATUS

editing

proposed

#4 by Michel Marcus at Sun Jul 14 04:15:39 EDT 2013

OFFSET

0,1,4

FORMULA

a(n) = A048984(n) - 1. Michel Marcus, Jul 14 2013

PROG

(PARI) lista(nn) = {forcomposite (n=1, nn, nb = 0; forcomposite(d=1, n-1, if (gcd(n, d) == 1, nb++)); print1(nb, ", "); ); } \\ Michel Marcus, Jul 14 2013

CROSSREFS

Cf. A000010, A048984, A002808.

STATUS

approved

editing

#3 by Russ Cox at Sat Mar 31 13:50:36 EDT 2012

AUTHOR

Naohiro Nomoto (6284968128(AT)geocities.co.jp)

Naohiro Nomoto

Discussion

Sat Mar 31

13:50

OEIS Server: https://oeis.org/edit/global/906

#2 by N. J. A. Sloane at Fri May 16 03:00:00 EDT 2003

NAME

As n runs through composite numbers, a(n) = no. number of composite d < n such that GCD(d,n) = 1.

KEYWORD

easy,nonn,new

AUTHOR

Naohiro Nomoto (6284968128@(AT)geocities.co.jp)

#1 by N. J. A. Sloane at Sat Dec 11 03:00:00 EST 1999

NAME

As n runs through composite numbers, a(n) = no. of composite d < n such that GCD(d,n) = 1.

DATA

0, 0, 0, 2, 1, 0, 1, 3, 2, 0, 1, 5, 3, 0, 11, 4, 9, 4, 0, 5, 10, 6, 14, 2, 7, 13, 5, 1, 7, 11, 9, 2, 27, 6, 18, 10, 3, 25, 9, 21, 13, 1, 13, 19, 14, 31, 4, 14, 26, 7, 5, 16, 20, 16, 40, 5, 11, 32, 19, 3, 42, 20, 34, 18, 2, 49, 21, 37, 23, 49, 9, 18

OFFSET

0,4

EXAMPLE

9 is 4th composite number, GCD(9,4)=GCD(9,8)=1, so a(4) = 2.

CROSSREFS

Cf. A000010, A048984.

KEYWORD

easy,nonn

AUTHOR

Naohiro Nomoto (6284968128@geocities.co.jp)

STATUS

approved