21500491 has 2 divisors, whose sum is σ = 21500492. Its totient is φ = 21500490.

The previous prime is 21500489. The next prime is 21500497. The reversal of 21500491 is 19400512.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21500491 - 2¹ = 21500489 is a prime.

It is a super-2 number, since 2×21500491² = 924542226482162, which contains 22 as substring.

Together with 21500489, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (21500497) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10750245 + 10750246.

It is an arithmetic number, because the mean of its divisors is an integer number (10750246).

Almost surely, 2^21500491 is an apocalyptic number.

21500491 is a deficient number, since it is larger than the sum of its proper divisors (1).

21500491 is an equidigital number, since it uses as much as digits as its factorization.

21500491 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 360, while the sum is 22.

The square root of 21500491 is about 4636.8621933372. The cubic root of 21500491 is about 278.0670050520.

The spelling of 21500491 in words is "twenty-one million, five hundred thousand, four hundred ninety-one".