21368591 has 2 divisors, whose sum is σ = 21368592.
Its totient is φ = 21368590.
The previous prime is 21368569. The next prime is 21368617. The reversal of 21368591 is 19586312.
It is a weak prime.
It is a cyclic number.
It is not a de Polignac number, because 21368591 - 26 = 21368527 is a 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 (21368531) by changing a digit.
It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10684295 + 10684296.
It is an arithmetic number, because the mean of its divisors is an integer number (10684296).
Almost surely, 221368591 is an apocalyptic number.
21368591 is a deficient number, since it is larger than the sum of its proper divisors (1).
21368591 is an equidigital number, since it uses as much as digits as its factorization.
21368591 is an evil number, because the sum of its binary digits is even.
The product of its digits is 12960, while the sum is 35.
The square root of 21368591 is about 4622.6173322048.
The cubic root of 21368591 is about 277.4972150249.
The spelling of 21368591 in words is "twenty-one million, three hundred sixty-eight thousand, five hundred ninety-one".