20978861 has 4 divisors (see below), whose sum is σ = 21702300. Its totient is φ = 20255424.

The previous prime is 20978843. The next prime is 20978863. The reversal of 20978861 is 16887902.

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 7946761 + 13032100 = 2819^2 + 3610^2 .

It is a cyclic number.

It is not a de Polignac number, because 20978861 - 2²² = 16784557 is a prime.

It is a super-2 number, since 2×20978861² = 880225217714642, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20978863) 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, 361676 + ... + 361733.

It is an arithmetic number, because the mean of its divisors is an integer number (5425575).

Almost surely, 2^20978861 is an apocalyptic number.

It is an amenable number.

20978861 is a deficient number, since it is larger than the sum of its proper divisors (723439).

20978861 is an equidigital number, since it uses as much as digits as its factorization.

20978861 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 723438.

The product of its (nonzero) digits is 48384, while the sum is 41.

The square root of 20978861 is about 4580.2686602425. The cubic root of 20978861 is about 275.7998137046.

The spelling of 20978861 in words is "twenty million, nine hundred seventy-eight thousand, eight hundred sixty-one".