20399981 has 4 divisors (see below), whose sum is σ = 23314272. Its totient is φ = 17485692.

The previous prime is 20399969. The next prime is 20399993. The reversal of 20399981 is 18999302.

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 an interprime number because it is at equal distance from previous prime (20399969) and next prime (20399993).

It is a de Polignac number, because none of the positive numbers 2^k-20399981 is a prime.

It is a super-2 number, since 2×20399981² = 832318449600722, 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 (20399921) 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, 1457135 + ... + 1457148.

It is an arithmetic number, because the mean of its divisors is an integer number (5828568).

Almost surely, 2^20399981 is an apocalyptic number.

It is an amenable number.

20399981 is a deficient number, since it is larger than the sum of its proper divisors (2914291).

20399981 is an equidigital number, since it uses as much as digits as its factorization.

20399981 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2914290.

The product of its (nonzero) digits is 34992, while the sum is 41.

The square root of 20399981 is about 4516.6338129186. The cubic root of 20399981 is about 273.2393567802.

The spelling of 20399981 in words is "twenty million, three hundred ninety-nine thousand, nine hundred eighty-one".