21357405 has 32 divisors (see below), whose sum is σ = 38171520. Its totient is φ = 11329920.

The previous prime is 21357403. The next prime is 21357431. The reversal of 21357405 is 50475312.

It is a happy number.

It is not a de Polignac number, because 21357405 - 2¹ = 21357403 is a prime.

It is a super-2 number, since 2×21357405² = 912277496668050, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21357403) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 37654 + ... + 38216.

It is an arithmetic number, because the mean of its divisors is an integer number (1192860).

Almost surely, 2^21357405 is an apocalyptic number.

It is an amenable number.

21357405 is a deficient number, since it is larger than the sum of its proper divisors (16814115).

21357405 is a wasteful number, since it uses less digits than its factorization.

21357405 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 858 (or 852 counting only the distinct ones).

The product of its (nonzero) digits is 4200, while the sum is 27.

The square root of 21357405 is about 4621.4072532076. The cubic root of 21357405 is about 277.4487852892.

The spelling of 21357405 in words is "twenty-one million, three hundred fifty-seven thousand, four hundred five".