21157061 has 4 divisors (see below), whose sum is σ = 22401612. Its totient is φ = 19912512.

The previous prime is 21157049. The next prime is 21157067. The reversal of 21157061 is 16075112.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 7392961 + 13764100 = 2719^2 + 3710^2 .

It is a cyclic number.

It is not a de Polignac number, because 21157061 - 2¹⁴ = 21140677 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21157067) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 622250 + ... + 622283.

It is an arithmetic number, because the mean of its divisors is an integer number (5600403).

Almost surely, 2^21157061 is an apocalyptic number.

It is an amenable number.

21157061 is a deficient number, since it is larger than the sum of its proper divisors (1244551).

21157061 is a wasteful number, since it uses less digits than its factorization.

21157061 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1244550.

The product of its (nonzero) digits is 420, while the sum is 23.

The square root of 21157061 is about 4599.6805323848. The cubic root of 21157061 is about 276.5785185547.

The spelling of 21157061 in words is "twenty-one million, one hundred fifty-seven thousand, sixty-one".