20521609 has 2 divisors, whose sum is σ = 20521610. Its totient is φ = 20521608.

The previous prime is 20521603. The next prime is 20521639. The reversal of 20521609 is 90612502.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 18088009 + 2433600 = 4253^2 + 1560^2 .

It is a cyclic number.

It is not a de Polignac number, because 20521609 - 2¹³ = 20513417 is a prime.

It is a super-2 number, since 2×20521609² = 842272871897762, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (20521603) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10260804 + 10260805.

It is an arithmetic number, because the mean of its divisors is an integer number (10260805).

Almost surely, 2^20521609 is an apocalyptic number.

It is an amenable number.

20521609 is a deficient number, since it is larger than the sum of its proper divisors (1).

20521609 is an equidigital number, since it uses as much as digits as its factorization.

20521609 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1080, while the sum is 25.

The square root of 20521609 is about 4530.0782553947. The cubic root of 20521609 is about 273.7813135993.

The spelling of 20521609 in words is "twenty million, five hundred twenty-one thousand, six hundred nine".