21523609 has 2 divisors, whose sum is σ = 21523610. Its totient is φ = 21523608.

The previous prime is 21523591. The next prime is 21523631. The reversal of 21523609 is 90632512.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21160000 + 363609 = 4600^2 + 603^2 .

It is a cyclic number.

It is not a de Polignac number, because 21523609 - 2²¹ = 19426457 is a prime.

It is not a weakly prime, because it can be changed into another prime (21523669) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10761804 + 10761805.

It is an arithmetic number, because the mean of its divisors is an integer number (10761805).

Almost surely, 2^21523609 is an apocalyptic number.

It is an amenable number.

21523609 is a deficient number, since it is larger than the sum of its proper divisors (1).

21523609 is an equidigital number, since it uses as much as digits as its factorization.

21523609 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 3240, while the sum is 28.

The square root of 21523609 is about 4639.3543731860. The cubic root of 21523609 is about 278.1666314653.

The spelling of 21523609 in words is "twenty-one million, five hundred twenty-three thousand, six hundred nine".