21154561 has 4 divisors (see below), whose sum is σ = 21163824. Its totient is φ = 21145300.

The previous prime is 21154547. The next prime is 21154577. The reversal of 21154561 is 16545112.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21154561 - 2¹³ = 21146369 is a prime.

It is a super-2 number, since 2×21154561² = 895030902205442, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21154591) 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, 1506 + ... + 6676.

It is an arithmetic number, because the mean of its divisors is an integer number (5290956).

Almost surely, 2^21154561 is an apocalyptic number.

It is an amenable number.

21154561 is a deficient number, since it is larger than the sum of its proper divisors (9263).

21154561 is an equidigital number, since it uses as much as digits as its factorization.

21154561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9262.

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

The square root of 21154561 is about 4599.4087663525. The cubic root of 21154561 is about 276.5676242637.

Adding to 21154561 its reverse (16545112), we get a palindrome (37699673).

The spelling of 21154561 in words is "twenty-one million, one hundred fifty-four thousand, five hundred sixty-one".