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A072297 Number of even non-cototients not exceeding 2^n. 0
0, 0, 0, 1, 2, 6, 10, 23, 48, 99, 194, 392, 791, 1600, 3290, 6810, 13900, 28269, 57455, 116213, 234237, 470861, 945510, 1897007, 3802257, 7616206, 15244011, 30493702, 60965480, 121838430, 243409121, 486131077, 970680425, 1937876841, 3868346975 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,5

LINKS

Table of n, a(n) for n=1..35.

EXAMPLE

a(6) = 6 because the even non-cototients not exceeding 64 are {10,26,34,50,52,58}.

MATHEMATICA

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

CROSSREFS

Number of terms in A063740 <= 2^n. Cf. A072077.

Sequence in context: A049750 A295139 A134016 * A183036 A120963 A200220

Adjacent sequences:  A072294 A072295 A072296 * A072298 A072299 A072300

KEYWORD

hard,nonn

AUTHOR

Robert G. Wilson v, Jul 13 2002 and Jul 29 2002

EXTENSIONS

a(16) and a(21) corrected and a(28)-a(32) from Donovan Johnson, Jun 23 2010

a(33)-a(35) from Donovan Johnson, Jun 03 2013

STATUS

approved

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Last modified April 23 02:14 EDT 2019. Contains 322380 sequences. (Running on oeis4.)