21512545 has 4 divisors (see below), whose sum is σ = 25815060. Its totient is φ = 17210032.

The previous prime is 21512539. The next prime is 21512591. The reversal of 21512545 is 54521512.

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 6697744 + 14814801 = 2588^2 + 3849^2 .

It is a cyclic number.

It is not a de Polignac number, because 21512545 - 2³ = 21512537 is a prime.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2151250 + ... + 2151259.

It is an arithmetic number, because the mean of its divisors is an integer number (6453765).

Almost surely, 2^21512545 is an apocalyptic number.

It is an amenable number.

21512545 is a deficient number, since it is larger than the sum of its proper divisors (4302515).

21512545 is an equidigital number, since it uses as much as digits as its factorization.

21512545 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4302514.

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

The square root of 21512545 is about 4638.1618126150. The cubic root of 21512545 is about 278.1189603536.

The spelling of 21512545 in words is "twenty-one million, five hundred twelve thousand, five hundred forty-five".