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A063830
a(n+1) is the smallest odd m whose cototient equals a(n).
0
1, 3, 9, 21, 45, 117, 297, 585, 1521, 3105, 6993, 14553, 43653, 90885, 185925, 397125, 847125, 1813125, 3238725, 7556829, 17253789, 36910365, 94571997, 220301277, 475043037, 47979336637, 183450404605, 525019294077
OFFSET
1,2
FORMULA
a(n) = Min{x, odd : A051953[ a(n-1) ]=a(n)}; a(1)=1; a(2)=3, least odd prime; a(n) = Min[ Select[ Range[ a, b ], Equal[ #-EulerPhi[ # ], a(n-1) ]& ] ].
EXAMPLE
a(5)=45, cototient(45) = 45 - Phi(45) = 45 - 24 = 21 = a(4). This iteration with even numbers might stop, like {1,2,4,6,10} does if the last computed number has no inverse cototient, like 10 which is a non-cototient number.
CROSSREFS
Sequence in context: A068156 A166452 A052101 * A062444 A141156 A262197
KEYWORD
nonn
AUTHOR
Labos Elemer, Aug 21 2001
EXTENSIONS
More terms from David Wasserman, Jul 23 2002
a(26)-a(28) from Donovan Johnson, Feb 06 2010
STATUS
approved