27644 is a member of OEIS A067796: numbers k such that euler_phi(k) + euler_phi(k+1) = k, here 27644 --> 13820

and 27645 --> 13824.

The sequence can be generated as follows:

INPUT

L=[]

for n in [1..40000]:

  if euler_phi(n)+euler_phi(n+1)==n:

    L.append(n)

    if n==27644:

      print(n,"-->",euler_phi(n))

      print(n+1,"-->",euler_phi(n+1))

print(L)

OUTPUT

27644 --> 13820

27645 --> 13824

[14, 20, 44, 140, 254, 272, 284, 344, 464, 764, 1224, 1424, 2064, 3200, 3824, 11648, 21584, 25520, 27644, 38840]

27644 is a nialpdrome in base 13 : c776.

27644 has an aliquot sequence that does not terminate after 101 steps.

27644 has a sum of squares that is equal to a square, here 121 = 11^2. In the range up to one million, there are 35179 or about 3.52% of numbers with this property.

27644 can be rendered as a digit equation as follows:

-2 + 7 = 6 - 4 / 4