21507901 has 4 divisors (see below), whose sum is σ = 21645052. Its totient is φ = 21370752.

The previous prime is 21507881. The next prime is 21507911. The reversal of 21507901 is 10970512.

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 14055001 + 7452900 = 3749^2 + 2730^2 .

It is a cyclic number.

It is not a de Polignac number, because 21507901 - 2⁹ = 21507389 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21507911) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 68340 + ... + 68653.

It is an arithmetic number, because the mean of its divisors is an integer number (5411263).

Almost surely, 2^21507901 is an apocalyptic number.

It is an amenable number.

21507901 is a deficient number, since it is larger than the sum of its proper divisors (137151).

21507901 is a wasteful number, since it uses less digits than its factorization.

21507901 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 137150.

The product of its (nonzero) digits is 630, while the sum is 25.

The square root of 21507901 is about 4637.6611562295. The cubic root of 21507901 is about 278.0989460255.

The spelling of 21507901 in words is "twenty-one million, five hundred seven thousand, nine hundred one".