

A245388


n such that n  tau(n) is a perfect square.


3



1, 2, 3, 4, 8, 11, 24, 83, 85, 125, 152, 156, 175, 227, 297, 365, 443, 445, 533, 584, 600, 629, 847, 924, 965, 969, 1036, 1091, 1304, 1308, 1458, 1523, 1612, 1685, 1800, 1853, 1960, 2027, 2316, 2340, 2409, 2605, 2716, 2813, 3029, 3251, 3729, 3973, 4108, 4233
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OFFSET

1,2


COMMENTS

n  tau(n) = A049820(n) is the number of positive integers < n that do not divide n.


LINKS

Robert Israel, Table of n, a(n) for n = 1..1000


EXAMPLE

4  tau(4) = 4  3 = 1^2 so 4 is in the sequence.


MAPLE

filter:= proc(n) local t;
t:= numtheory:tau(n);
issqr(nt)
end proc;
select(filter, [$1..10^4]);


MATHEMATICA

Select[Range[10^4], IntegerQ[Sqrt[#  DivisorSigma[0, #]]]&] (* JeanFrançois Alcover, Apr 12 2019 *)


PROG

(Sage)
def is_A245388(n):
a = sloane.A000005
return is_square(n  a(n))
A245388_list = lambda up_to: filter(is_A245388, (1..up_to))
A245388_list(4333) # Peter Luschny, Jul 20 2014


CROSSREFS

Cf. A000005, A049820, A245197
Sequence in context: A269797 A280195 A286224 * A164573 A064418 A171164
Adjacent sequences: A245385 A245386 A245387 * A245389 A245390 A245391


KEYWORD

nonn


AUTHOR

Robert Israel, Jul 20 2014


STATUS

approved



