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A305026 Numbers k such that sopfr(k) = tau(k)^2. 2
39, 55, 354, 578, 1634, 1644, 6604, 8253, 9825, 12573, 13516, 14749, 15244, 16684, 18669, 18672, 19276, 19564, 21032, 22225, 25305, 28449, 29853, 31688, 33633, 35793, 41261, 41768, 41949, 42813, 48013, 50670, 54048, 59750, 60804, 63609, 63869, 65265, 78832 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

For numbers k that satisfy the condition, tau(k) will always be even because tau(k) is odd only if k is a square, but if k is a square then sopfr(k) is even (because every prime appears with an even exponent) and thus it cannot be equal to tau(k)^2 which is odd as tau(k). - Giovanni Resta, May 24 2018

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..1000

FORMULA

k such that A001414(k) = A000005(k)^2.

MATHEMATICA

Rest@ Select[Range[10^5], Total[Times @@@ FactorInteger@ #] == DivisorSigma[0, #]^2 &] (* Michael De Vlieger, May 27 2018 *)

PROG

(PARI) isok(n) = my(f=factor(n)); sum(k=1, #f~, f[k, 1]*f[k, 2]) == numdiv(n)^2; \\ Michel Marcus, May 24 2018

CROSSREFS

Cf. A000005, A001414, A078511.

Sequence in context: A165346 A268083 A063480 * A009633 A327586 A156333

Adjacent sequences:  A305023 A305024 A305025 * A305027 A305028 A305029

KEYWORD

nonn

AUTHOR

Parker Grootenhuis, May 23 2018

STATUS

approved

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Last modified April 11 21:52 EDT 2021. Contains 342888 sequences. (Running on oeis4.)