20981251 has 4 divisors (see below), whose sum is σ = 21294472. Its totient is φ = 20668032.

The previous prime is 20981249. The next prime is 20981273. The reversal of 20981251 is 15218902.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 15218902 = 2 ⋅7609451.

It is a cyclic number.

It is not a de Polignac number, because 20981251 - 2¹ = 20981249 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20981201) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 156510 + ... + 156643.

It is an arithmetic number, because the mean of its divisors is an integer number (5323618).

Almost surely, 2^20981251 is an apocalyptic number.

20981251 is a deficient number, since it is larger than the sum of its proper divisors (313221).

20981251 is an equidigital number, since it uses as much as digits as its factorization.

20981251 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 313220.

The product of its (nonzero) digits is 1440, while the sum is 28.

The square root of 20981251 is about 4580.5295545384. The cubic root of 20981251 is about 275.8102867315.

The spelling of 20981251 in words is "twenty million, nine hundred eighty-one thousand, two hundred fifty-one".