21509995 has 16 divisors (see below), whose sum is σ = 29262240. Its totient is φ = 15047424.

The previous prime is 21509989. The next prime is 21510007. The reversal of 21509995 is 59990512.

It is a cyclic number.

It is not a de Polignac number, because 21509995 - 2⁵ = 21509963 is a prime.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 7474 + ... + 9943.

It is an arithmetic number, because the mean of its divisors is an integer number (1828890).

Almost surely, 2^21509995 is an apocalyptic number.

21509995 is a deficient number, since it is larger than the sum of its proper divisors (7752245).

21509995 is a wasteful number, since it uses less digits than its factorization.

21509995 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 17454.

The product of its (nonzero) digits is 36450, while the sum is 40.

The square root of 21509995 is about 4637.8869110835. The cubic root of 21509995 is about 278.1079709306.

The spelling of 21509995 in words is "twenty-one million, five hundred nine thousand, nine hundred ninety-five".