21145778 has 4 divisors (see below), whose sum is σ = 31718670. Its totient is φ = 10572888.

The previous prime is 21145771. The next prime is 21145799. The reversal of 21145778 is 87754112.

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

It can be written as a sum of positive squares in only one way, i.e., 17197609 + 3948169 = 4147^2 + 1987^2 .

It is not an unprimeable number, because it can be changed into a prime (21145771) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5286443 + ... + 5286446.

Almost surely, 2^21145778 is an apocalyptic number.

21145778 is a deficient number, since it is larger than the sum of its proper divisors (10572892).

21145778 is a wasteful number, since it uses less digits than its factorization.

21145778 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10572891.

The product of its digits is 15680, while the sum is 35.

The square root of 21145778 is about 4598.4538705961. The cubic root of 21145778 is about 276.5293436349.

The spelling of 21145778 in words is "twenty-one million, one hundred forty-five thousand, seven hundred seventy-eight".