21515401 has 4 divisors (see below), whose sum is σ = 21712900. Its totient is φ = 21317904.

The previous prime is 21515381. The next prime is 21515411. The reversal of 21515401 is 10451512.

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 18361225 + 3154176 = 4285^2 + 1776^2 .

It is a cyclic number.

It is not a de Polignac number, because 21515401 - 2⁵ = 21515369 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21515411) 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, 98586 + ... + 98803.

It is an arithmetic number, because the mean of its divisors is an integer number (5428225).

Almost surely, 2^21515401 is an apocalyptic number.

It is an amenable number.

21515401 is a deficient number, since it is larger than the sum of its proper divisors (197499).

21515401 is a wasteful number, since it uses less digits than its factorization.

21515401 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 197498.

The product of its (nonzero) digits is 200, while the sum is 19.

The square root of 21515401 is about 4638.4696829881. The cubic root of 21515401 is about 278.1312674765.

Adding to 21515401 its reverse (10451512), we get a palindrome (31966913).

The spelling of 21515401 in words is "twenty-one million, five hundred fifteen thousand, four hundred one".