21520391 has 2 divisors, whose sum is σ = 21520392. Its totient is φ = 21520390.

The previous prime is 21520363. The next prime is 21520399. The reversal of 21520391 is 19302512.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21520391 - 2²² = 17326087 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21520399) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10760195 + 10760196.

It is an arithmetic number, because the mean of its divisors is an integer number (10760196).

Almost surely, 2^21520391 is an apocalyptic number.

21520391 is a deficient number, since it is larger than the sum of its proper divisors (1).

21520391 is an equidigital number, since it uses as much as digits as its factorization.

21520391 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 540, while the sum is 23.

The square root of 21520391 is about 4639.0075447233. The cubic root of 21520391 is about 278.1527678542.

The spelling of 21520391 in words is "twenty-one million, five hundred twenty thousand, three hundred ninety-one".