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A077646 Solutions to lcm(n, tau(n)) = 2n which are neither prime nor twice a prime, where tau(k) = d(k) is the number of divisors of k. 2
45, 63, 75, 90, 99, 117, 120, 126, 147, 150, 153, 168, 171, 198, 207, 216, 234, 243, 261, 264, 279, 280, 294, 306, 312, 333, 342, 363, 369, 387, 405, 408, 414, 420, 423, 440, 456, 477, 486, 507, 520, 522, 531, 540, 549, 552, 558, 603, 616, 639, 657, 660 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

FORMULA

Composite solutions to A009530(x)=2x which are not twice a prime.

EXAMPLE

n=63: d(n) = tau(n) = 6, lcm(63,6) = 126 = 2n.

PROG

(PARI) is(n)=!isprime(if(n%2, n, n/2)) && lcm(n, numdiv(n))==2*n \\ Charles R Greathouse IV, Oct 28 2013

CROSSREFS

Cf. A009530, A001747, A000040, A065091.

Sequence in context: A140277 A242263 A242264 * A230577 A175761 A046364

Adjacent sequences:  A077643 A077644 A077645 * A077647 A077648 A077649

KEYWORD

nonn

AUTHOR

Labos Elemer, Nov 18 2002

STATUS

approved

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Last modified September 17 22:53 EDT 2019. Contains 327147 sequences. (Running on oeis4.)