21071609 has 4 divisors (see below), whose sum is σ = 22692516. Its totient is φ = 19450704.

The previous prime is 21071587. The next prime is 21071621. The reversal of 21071609 is 90617012.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 6017209 + 15054400 = 2453^2 + 3880^2 .

It is not a de Polignac number, because 21071609 - 2¹² = 21067513 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21071009) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 810434 + ... + 810459.

It is an arithmetic number, because the mean of its divisors is an integer number (5673129).

Almost surely, 2^21071609 is an apocalyptic number.

It is an amenable number.

21071609 is a deficient number, since it is larger than the sum of its proper divisors (1620907).

21071609 is a wasteful number, since it uses less digits than its factorization.

21071609 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1620906.

The product of its (nonzero) digits is 756, while the sum is 26.

The square root of 21071609 is about 4590.3822280939. The cubic root of 21071609 is about 276.2056552012.

The spelling of 21071609 in words is "twenty-one million, seventy-one thousand, six hundred nine".