A072297 Number of even non-cototients not exceeding 2^n.

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

Offset: 1

Author

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

Keywords

• hard
• nonn

Examples

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

Crossrefs

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

Programs

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}]

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