20977981 has 4 divisors (see below), whose sum is σ = 21333600. Its totient is φ = 20622364.

The previous prime is 20977967. The next prime is 20978011. The reversal of 20977981 is 18977902.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20977981 is a prime.

It is a super-2 number, since 2×20977981² = 880151373672722, 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 (20977951) 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, 177721 + ... + 177838.

It is an arithmetic number, because the mean of its divisors is an integer number (5333400).

Almost surely, 2^20977981 is an apocalyptic number.

It is an amenable number.

20977981 is a deficient number, since it is larger than the sum of its proper divisors (355619).

20977981 is an equidigital number, since it uses as much as digits as its factorization.

20977981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 355618.

The product of its (nonzero) digits is 63504, while the sum is 43.

The square root of 20977981 is about 4580.1725950012. The cubic root of 20977981 is about 275.7959573270.

The spelling of 20977981 in words is "twenty million, nine hundred seventy-seven thousand, nine hundred eighty-one".