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A072077 Number of even nontotients not exceeding 2^n. 1
0, 0, 0, 1, 2, 6, 17, 41, 94, 215, 470, 1004, 2126, 4449, 9278, 19177, 39388, 80698, 164808, 335809, 683117, 1387415, 2813664, 5700228, 11536241, 23324624, 47122764, 95134678, 191937316, 387024829, 780018815, 1571331010 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,5

LINKS

Table of n, a(n) for n=1..32.

EXAMPLE

n = 6: a(6) = 6 because the even nontotients not exceeding 64 are {14,26,34,38,50,62}.

MATHEMATICA

a = Table[0, {2^26}]; Do[ b = EulerPhi[n]; If[ EvenQ[b] && b < 2^27, a[[b/2]]++ ], {n, 3, 10^9}]; c = 0; k = 1; Do[ While[k <= 2^n, If[ a[[k]] == 0, c++ ]; k++ ]; Print[c], {n, 1, 17}]

CROSSREFS

Number of terms in A005277 <= 2^n.

Sequence in context: A239234 A192707 A252814 * A229732 A130104 A014833

Adjacent sequences:  A072074 A072075 A072076 * A072078 A072079 A072080

KEYWORD

nonn,hard

AUTHOR

Labos Elemer, Jun 13 2002

EXTENSIONS

Edited and extended by Robert G. Wilson v, Jul 15 2002

a(27)-a(32) from Donovan Johnson, Jun 03 2013

STATUS

approved

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Last modified August 15 00:32 EDT 2020. Contains 336484 sequences. (Running on oeis4.)