21512455 has 4 divisors (see below), whose sum is σ = 25814952. Its totient is φ = 17209960.

The previous prime is 21512431. The next prime is 21512459. The reversal of 21512455 is 55421512.

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

It is not a de Polignac number, because 21512455 - 2⁹ = 21511943 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 (21512459) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2151241 + ... + 2151250.

It is an arithmetic number, because the mean of its divisors is an integer number (6453738).

Almost surely, 2^21512455 is an apocalyptic number.

21512455 is a deficient number, since it is larger than the sum of its proper divisors (4302497).

21512455 is an equidigital number, since it uses as much as digits as its factorization.

21512455 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4302496.

The product of its digits is 2000, while the sum is 25.

The square root of 21512455 is about 4638.1521104854. The cubic root of 21512455 is about 278.1185725064.

Adding to 21512455 its reverse (55421512), we get a palindrome (76933967).

The spelling of 21512455 in words is "twenty-one million, five hundred twelve thousand, four hundred fifty-five".