21640499 has 2 divisors, whose sum is σ = 21640500. Its totient is φ = 21640498.

The previous prime is 21640477. The next prime is 21640501. The reversal of 21640499 is 99404612.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21640499 - 2¹⁶ = 21574963 is a prime.

It is a super-2 number, since 2×21640499² = 936622393938002, which contains 22 as substring.

Together with 21640501, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21640469) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10820249 + 10820250.

It is an arithmetic number, because the mean of its divisors is an integer number (10820250).

Almost surely, 2^21640499 is an apocalyptic number.

21640499 is a deficient number, since it is larger than the sum of its proper divisors (1).

21640499 is an equidigital number, since it uses as much as digits as its factorization.

21640499 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 15552, while the sum is 35.

The square root of 21640499 is about 4651.9349737502. The cubic root of 21640499 is about 278.6692766316.

The spelling of 21640499 in words is "twenty-one million, six hundred forty thousand, four hundred ninety-nine".