21051391 has 2 divisors, whose sum is σ = 21051392. Its totient is φ = 21051390.

The previous prime is 21051383. The next prime is 21051397. The reversal of 21051391 is 19315012.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21051391 - 2³ = 21051383 is a prime.

It is a super-2 number, since 2×21051391² = 886322126069762, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21051397) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10525695 + 10525696.

It is an arithmetic number, because the mean of its divisors is an integer number (10525696).

Almost surely, 2^21051391 is an apocalyptic number.

21051391 is a deficient number, since it is larger than the sum of its proper divisors (1).

21051391 is an equidigital number, since it uses as much as digits as its factorization.

21051391 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 270, while the sum is 22.

The square root of 21051391 is about 4588.1794864630. The cubic root of 21051391 is about 276.1172880698.

The spelling of 21051391 in words is "twenty-one million, fifty-one thousand, three hundred ninety-one".