login
A072077
Number of even nontotients not exceeding 2^n.
2
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, 3164113363
OFFSET
1,5
COMMENTS
Number of terms in A005277 <= 2^n.
EXAMPLE
For 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}]
PROG
(PARI) lista(kmax) = {my(c = 0, p = 2); forstep(k = 2, kmax, 2, if(!istotient(k), c++); if(k == p, print1(c, ", "); p *= 2)); } \\ Amiram Eldar, Jun 20 2024
CROSSREFS
Sequence in context: A239234 A192707 A252814 * A229732 A130104 A014833
KEYWORD
nonn,hard,more
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
a(33) from Amiram Eldar, Jun 20 2024
STATUS
approved