51021391 has 2 divisors, whose sum is σ = 51021392. Its totient is φ = 51021390.

The previous prime is 51021331. The next prime is 51021401. The reversal of 51021391 is 19312015.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 51021391 - 2¹¹ = 51019343 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (51021331) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 25510695 + 25510696.

It is an arithmetic number, because the mean of its divisors is an integer number (25510696).

Almost surely, 2^51021391 is an apocalyptic number.

51021391 is a deficient number, since it is larger than the sum of its proper divisors (1).

51021391 is an equidigital number, since it uses as much as digits as its factorization.

51021391 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 51021391 is about 7142.9259410972. The cubic root of 51021391 is about 370.8948174057.

The spelling of 51021391 in words is "fifty-one million, twenty-one thousand, three hundred ninety-one".