21798509 has 2 divisors, whose sum is σ = 21798510. Its totient is φ = 21798508.

The previous prime is 21798499. The next prime is 21798521. The reversal of 21798509 is 90589712.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 19333609 + 2464900 = 4397^2 + 1570^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21798509 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21798559) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10899254 + 10899255.

It is an arithmetic number, because the mean of its divisors is an integer number (10899255).

Almost surely, 2^21798509 is an apocalyptic number.

It is an amenable number.

21798509 is a deficient number, since it is larger than the sum of its proper divisors (1).

21798509 is an equidigital number, since it uses as much as digits as its factorization.

21798509 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 45360, while the sum is 41.

The square root of 21798509 is about 4668.8873406841. The cubic root of 21798509 is about 279.3458752610.

The spelling of 21798509 in words is "twenty-one million, seven hundred ninety-eight thousand, five hundred nine".