20951921 has 2 divisors, whose sum is σ = 20951922. Its totient is φ = 20951920.

The previous prime is 20951899. The next prime is 20951923. The reversal of 20951921 is 12915902.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 13987600 + 6964321 = 3740^2 + 2639^2 .

It is a cyclic number.

It is not a de Polignac number, because 20951921 - 2¹⁸ = 20689777 is a prime.

Together with 20951923, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (20951923) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10475960 + 10475961.

It is an arithmetic number, because the mean of its divisors is an integer number (10475961).

Almost surely, 2^20951921 is an apocalyptic number.

It is an amenable number.

20951921 is a deficient number, since it is larger than the sum of its proper divisors (1).

20951921 is an equidigital number, since it uses as much as digits as its factorization.

20951921 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1620, while the sum is 29.

The square root of 20951921 is about 4577.3268399799. The cubic root of 20951921 is about 275.6817070435.

The spelling of 20951921 in words is "twenty million, nine hundred fifty-one thousand, nine hundred twenty-one".