21081609 has 6 divisors (see below), whose sum is σ = 30451226. Its totient is φ = 14054400.

The previous prime is 21081589. The next prime is 21081611. The reversal of 21081609 is 90618012.

It can be written as a sum of positive squares in only one way, i.e., 14175225 + 6906384 = 3765^2 + 2628^2 .

It is not a de Polignac number, because 21081609 - 2⁸ = 21081353 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21081679) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1171192 + ... + 1171209.

Almost surely, 2^21081609 is an apocalyptic number.

It is an amenable number.

21081609 is a deficient number, since it is larger than the sum of its proper divisors (9369617).

21081609 is a wasteful number, since it uses less digits than its factorization.

21081609 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2342407 (or 2342404 counting only the distinct ones).

The product of its (nonzero) digits is 864, while the sum is 27.

The square root of 21081609 is about 4591.4713328083. The cubic root of 21081609 is about 276.2493414670.

The spelling of 21081609 in words is "twenty-one million, eighty-one thousand, six hundred nine".