21651541 has 4 divisors (see below), whose sum is σ = 21732300. Its totient is φ = 21570784.

The previous prime is 21651529. The next prime is 21651551. The reversal of 21651541 is 14515612.

It is a happy number.

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 12103441 + 9548100 = 3479^2 + 3090^2 .

It is a cyclic number.

It is not a de Polignac number, because 21651541 - 2²³ = 13262933 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21651551) 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, 39976 + ... + 40513.

It is an arithmetic number, because the mean of its divisors is an integer number (5433075).

Almost surely, 2^21651541 is an apocalyptic number.

It is an amenable number.

21651541 is a deficient number, since it is larger than the sum of its proper divisors (80759).

21651541 is an equidigital number, since it uses as much as digits as its factorization.

21651541 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 80758.

The product of its digits is 1200, while the sum is 25.

The square root of 21651541 is about 4653.1216403614. The cubic root of 21651541 is about 278.7166652946.

The spelling of 21651541 in words is "twenty-one million, six hundred fifty-one thousand, five hundred forty-one".