21509464451 has 4 divisors (see below), whose sum is σ = 21532035672. Its totient is φ = 21486893232.

The previous prime is 21509464441. The next prime is 21509464453. The reversal of 21509464451 is 15446490512.

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

It is a cyclic number.

It is not a de Polignac number, because 21509464451 - 2³⁴ = 4329595267 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21509464399 and 21509464408.

It is not an unprimeable number, because it can be changed into a prime (21509464453) 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, 11284181 + ... + 11286086.

It is an arithmetic number, because the mean of its divisors is an integer number (5383008918).

Almost surely, 2^21509464451 is an apocalyptic number.

21509464451 is a deficient number, since it is larger than the sum of its proper divisors (22571221).

21509464451 is an equidigital number, since it uses as much as digits as its factorization.

21509464451 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 22571220.

The product of its (nonzero) digits is 172800, while the sum is 41.

The spelling of 21509464451 in words is "twenty-one billion, five hundred nine million, four hundred sixty-four thousand, four hundred fifty-one".