The On-Line Encyclopedia of Integer Sequences (OEIS)

Revision History for A039768

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A039768

Numbers k such that gcd(phi(k), k-1) = number of divisors of (k-1).
(history; published version)

#10 by Alois P. Heinz at Fri Oct 25 21:31:04 EDT 2019

STATUS

proposed

approved

#9 by Jon E. Schoenfield at Fri Oct 25 21:23:03 EDT 2019

STATUS

editing

proposed

#8 by Jon E. Schoenfield at Fri Oct 25 21:23:00 EDT 2019

NAME

GCDNumbers k such that gcd(phi(a(n)),a(nk), k-1) = number of divisors of (a(n)k-1).

STATUS

approved

editing

#7 by Alois P. Heinz at Wed Aug 28 16:36:09 EDT 2019

STATUS

proposed

approved

#6 by Amiram Eldar at Wed Aug 28 16:30:03 EDT 2019

STATUS

editing

proposed

#5 by Amiram Eldar at Wed Aug 28 16:13:02 EDT 2019

LINKS

Amiram Eldar, <a href="/A039768/b039768.txt">Table of n, a(n) for n = 1..10000</a>

MATHEMATICA

aQ[n_] := GCD[EulerPhi[n], n - 1] == DivisorSigma[0, n - 1]; Select[Range[2, 2110], aQ] (* Amiram Eldar, Aug 28 2019 *)

STATUS

approved

editing

#4 by Russ Cox at Fri Mar 30 17:20:56 EDT 2012

AUTHOR

Olivier Gerard (olivier.gerard(AT)gmail.com)

Olivier Gérard

Discussion

Fri Mar 30

17:20

OEIS Server: https://oeis.org/edit/global/117

#3 by N. J. A. Sloane at Fri Jan 09 03:00:00 EST 2009

KEYWORD

nonn,easy,new

AUTHOR

Olivier Gerard (ogerardolivier.gerard(AT)ext.jussieugmail.frcom)

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

CROSSREFS

Cf. A000005, A000010.

KEYWORD

nonn,easy,new

AUTHOR

Olivier Gerard (ogerard@(AT)ext.jussieu.fr)

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

NAME

GCD(phi(a(n)),a(n)-1) = number of divisors of (a(n)-1).

DATA

2, 3, 105, 133, 153, 185, 345, 377, 425, 585, 637, 665, 777, 805, 825, 873, 897, 905, 949, 1017, 1090, 1113, 1209, 1225, 1261, 1305, 1309, 1385, 1449, 1525, 1545, 1573, 1645, 1681, 1785, 1813, 1833, 1865, 1885, 1957, 1981, 2009, 2057, 2077, 2105

OFFSET

1,1

EXAMPLE

phi(105)=48, gcd(48,104)=8, 104 is divisible by {1,2,4,8,13,26,52,104}.

CROSSREFS

Cf. A000005,A000010

KEYWORD

nonn,easy

AUTHOR

Olivier Gerard ([email protected])

STATUS

approved