21630391 has 2 divisors, whose sum is σ = 21630392. Its totient is φ = 21630390.

The previous prime is 21630383. The next prime is 21630421. The reversal of 21630391 is 19303612.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21630391 - 2³ = 21630383 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21630991) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10815195 + 10815196.

It is an arithmetic number, because the mean of its divisors is an integer number (10815196).

Almost surely, 2^21630391 is an apocalyptic number.

21630391 is a deficient number, since it is larger than the sum of its proper divisors (1).

21630391 is an equidigital number, since it uses as much as digits as its factorization.

21630391 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 972, while the sum is 25.

The square root of 21630391 is about 4650.8484172245. The cubic root of 21630391 is about 278.6258822575.

The spelling of 21630391 in words is "twenty-one million, six hundred thirty thousand, three hundred ninety-one".