21491201 has 2 divisors, whose sum is σ = 21491202. Its totient is φ = 21491200.

The previous prime is 21491189. The next prime is 21491209. The reversal of 21491201 is 10219412.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18931201 + 2560000 = 4351^2 + 1600^2 .

It is a cyclic number.

It is not a de Polignac number, because 21491201 - 2¹⁰ = 21490177 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (21491209) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10745600 + 10745601.

It is an arithmetic number, because the mean of its divisors is an integer number (10745601).

Almost surely, 2^21491201 is an apocalyptic number.

It is an amenable number.

21491201 is a deficient number, since it is larger than the sum of its proper divisors (1).

21491201 is an equidigital number, since it uses as much as digits as its factorization.

21491201 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 144, while the sum is 20.

The square root of 21491201 is about 4635.8603300790. The cubic root of 21491201 is about 278.0269499260.

The spelling of 21491201 in words is "twenty-one million, four hundred ninety-one thousand, two hundred one".