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URL: https://oeis.org/A373437

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A373437
Integers k such that sigma(sigma(2*k))=2*sigma(sigma(k)); sigma=A000203.
0
2, 6, 14, 18, 38, 42, 50, 54, 62, 74, 86, 114, 122, 126, 134, 146, 150, 158, 162, 186, 206, 218, 222, 254, 258, 266, 302, 314, 326, 342, 350, 366, 378, 386, 398, 402, 422, 434, 438, 450, 458, 474, 482, 518, 542, 554, 558, 566, 578, 602, 618, 626, 654, 662, 666, 674, 686, 734, 746, 758, 762, 774, 794
OFFSET
1,1
LINKS
Graeme L. Cohen and H. J. J. te Riele, Iterating the sum-of-divisors function, Exp. Math., 5 (1996), 91-100.
MAPLE
with(numtheory):
P := proc (q)
local n, result:
result := []:
for n to q do
if sigma(sigma(2*n)) = 2*sigma(sigma(n)) then
result := [op(result), n]:
end if
end do:
print(result):
end proc:
P(10^3);
MATHEMATICA
Select[Range[800], DivisorSigma[1, DivisorSigma[1, 2#]]==2DivisorSigma[1, DivisorSigma[1, #]]&] (* Stefano Spezia, Jun 05 2024 *)
PROG
(Python)
from sympy import divisor_sigma as sigma
def P(q):
result = []
for n in range(1, q + 1):
if sigma(sigma(2 * n)) == 2 * sigma(sigma(n)):
result.append(n)
print(result)
P(10**3)
CROSSREFS
Sequence in context: A186299 A163777 A215807 * A140525 A189804 A308394
KEYWORD
nonn
AUTHOR
Rafik Khalfi, Jun 04 2024
STATUS
approved