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A068564
Numbers k such that phi(k) = 2*tau(k)^2.
0
51, 117, 148, 255, 585, 608, 740, 876, 2000, 2912, 3040, 3552, 3876, 3978, 4380, 6528, 7776, 8892, 9324, 14560, 14688, 14976, 15912, 17760, 18564, 19380, 19890, 32640, 38304, 38880, 44460, 46620, 73440, 74880, 79560, 92820, 118800, 126000, 191520
OFFSET
1,1
COMMENTS
There are no more terms below 10^9. This sequence is probably complete. - Amiram Eldar, Apr 29 2022
MATHEMATICA
Select[Range[10^5], EulerPhi[#] == 2*DivisorSigma[0, #]^2 &] (* Amiram Eldar, Apr 29 2022 *)
PROG
(Python)
from sympy import totient as phi, divisor_count as tau
def ok(n): return phi(n) == 2*tau(n)**2
print([k for k in range(1, 191521) if ok(k)]) # Michael S. Branicky, Apr 29 2022
CROSSREFS
Sequence in context: A044238 A044619 A031894 * A063314 A129298 A065010
KEYWORD
easy,nonn
AUTHOR
Benoit Cloitre, Mar 25 2002
EXTENSIONS
a(37)-a(39) from Amiram Eldar, Apr 29 2022
STATUS
approved