21078161 has 4 divisors (see below), whose sum is σ = 22699572. Its totient is φ = 19456752.

The previous prime is 21078149. The next prime is 21078179. The reversal of 21078161 is 16187012.

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 4227136 + 16851025 = 2056^2 + 4105^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21078161 is a prime.

It is a super-2 number, since 2×21078161² = 888577742283842, which contains 22 as substring.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21078161.

It is not an unprimeable number, because it can be changed into a prime (21078121) 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, 810686 + ... + 810711.

It is an arithmetic number, because the mean of its divisors is an integer number (5674893).

Almost surely, 2^21078161 is an apocalyptic number.

It is an amenable number.

21078161 is a deficient number, since it is larger than the sum of its proper divisors (1621411).

21078161 is a wasteful number, since it uses less digits than its factorization.

21078161 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1621410.

The product of its (nonzero) digits is 672, while the sum is 26.

The square root of 21078161 is about 4591.0958386860. The cubic root of 21078161 is about 276.2342800034.

The spelling of 21078161 in words is "twenty-one million, seventy-eight thousand, one hundred sixty-one".