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Revision History for A078640

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A078640

Number of numbers between 1 and n-1 that are coprime to n(n+1)(n+2).
(history; published version)

#13 by Harvey P. Dale at Sat May 07 11:02:06 EDT 2016

STATUS

editing

approved

#12 by Harvey P. Dale at Sat May 07 11:01:58 EDT 2016

MATHEMATICA

Table[Count[Range[1, n-1], _?(CoprimeQ[#, (n(n+1)(n+2))]&)], {n, 80}] (* Harvey P. Dale, May 07 2016 *)

STATUS

approved

editing

#11 by Michael Somos at Mon Mar 17 22:34:59 EDT 2014

STATUS

proposed

approved

#10 by Wesley Ivan Hurt at Mon Mar 17 22:18:10 EDT 2014

STATUS

editing

proposed

#9 by Wesley Ivan Hurt at Mon Mar 17 22:17:28 EDT 2014

EXAMPLE

a(10) is the number of numbers between 1 and 9 that are coprime to 10.*11.*12, which leaves 1 and 7, hence a(10) = 2.

STATUS

proposed

editing

#8 by Michel Marcus at Mon Mar 17 17:07:17 EDT 2014

STATUS

editing

proposed

Discussion

Mon Mar 17

21:43

Franklin T. Adams-Watters: I wonder if an earlier version of this sequence might have had between 1 and n instead of 1 and n-1. That would affect a(1) only. With the current definition, I agree that a(1) = 0 is correct.

#7 by Michel Marcus at Mon Mar 17 17:06:22 EDT 2014

EXTENSIONS

More terms from Michel Marcus, Mar 17 2014

Discussion

Mon Mar 17

17:07

Michel Marcus: I find a(1)=0 instead of 1. Looks ok to me. 
Is it OK ?

#6 by Michel Marcus at Mon Mar 17 17:05:57 EDT 2014

DATA

1, 0, 1, 1, 1, 1, 2, 2, 2, 2, 2, 3, 3, 2, 3, 4, 5, 5, 5, 4, 4, 5, 6, 6, 6, 6, 7, 8, 6, 7, 8, 9, 9, 6, 7, 8, 11, 10, 8, 9, 9, 11, 11, 10, 10, 11, 14, 13, 12, 11, 12, 15, 16, 13, 12, 11, 14, 17, 14, 15, 15, 16, 17, 14, 15, 15, 19, 20, 14, 15, 16, 23, 23, 18, 18

PROG

(PARI) a(n) = sum(i=1, n-1, gcd(i, n*(n+1)*(n+2)) == 1); \\ Michel Marcus, Mar 17 2014

STATUS

approved

editing

#5 by Russ Cox at Sat Mar 31 13:21:55 EDT 2012

AUTHOR

_Jon Perry (perry(AT)globalnet.co.uk), _, Dec 12 2002

Discussion

Sat Mar 31

13:21

OEIS Server: https://oeis.org/edit/global/886

#4 by N. J. A. Sloane at Wed Sep 22 03:00:00 EDT 2004

NAME

Numbers Number of numbers between 1 and n-1 that are coprime to n(n+1)(n+2).

KEYWORD

nonn,new

nonn