21191545 has 4 divisors (see below), whose sum is σ = 25429860. Its totient is φ = 16953232.

The previous prime is 21191543. The next prime is 21191557. The reversal of 21191545 is 54519112.

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 13017664 + 8173881 = 3608^2 + 2859^2 .

It is a cyclic number.

It is not a de Polignac number, because 21191545 - 2¹ = 21191543 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21191543) 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, 2119150 + ... + 2119159.

It is an arithmetic number, because the mean of its divisors is an integer number (6357465).

Almost surely, 2^21191545 is an apocalyptic number.

It is an amenable number.

21191545 is a deficient number, since it is larger than the sum of its proper divisors (4238315).

21191545 is an equidigital number, since it uses as much as digits as its factorization.

21191545 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4238314.

The product of its digits is 1800, while the sum is 28.

The square root of 21191545 is about 4603.4275273974. The cubic root of 21191545 is about 276.7287025612.

It can be divided in two parts, 21191 and 545, that added together give a triangular number (21736 = T₂₀₈).

The spelling of 21191545 in words is "twenty-one million, one hundred ninety-one thousand, five hundred forty-five".