20665261 has 2 divisors, whose sum is σ = 20665262. Its totient is φ = 20665260.

The previous prime is 20665259. The next prime is 20665273. The reversal of 20665261 is 16256602.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20196036 + 469225 = 4494^2 + 685^2 .

It is a cyclic number.

It is not a de Polignac number, because 20665261 - 2¹ = 20665259 is a prime.

Together with 20665259, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20665291) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10332630 + 10332631.

It is an arithmetic number, because the mean of its divisors is an integer number (10332631).

Almost surely, 2^20665261 is an apocalyptic number.

It is an amenable number.

20665261 is a deficient number, since it is larger than the sum of its proper divisors (1).

20665261 is an equidigital number, since it uses as much as digits as its factorization.

20665261 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 4320, while the sum is 28.

The square root of 20665261 is about 4545.9059603120. The cubic root of 20665261 is about 274.4186551093.

It can be divided in two parts, 20 and 665261, that added together give a triangular number (665281 = T₁₁₅₃).

The spelling of 20665261 in words is "twenty million, six hundred sixty-five thousand, two hundred sixty-one".