21561455 has 4 divisors (see below), whose sum is σ = 25873752. Its totient is φ = 17249160.

The previous prime is 21561443. The next prime is 21561469. The reversal of 21561455 is 55416512.

It is a happy number.

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

It is not a de Polignac number, because 21561455 - 2¹⁰ = 21560431 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2156141 + ... + 2156150.

It is an arithmetic number, because the mean of its divisors is an integer number (6468438).

Almost surely, 2^21561455 is an apocalyptic number.

21561455 is a deficient number, since it is larger than the sum of its proper divisors (4312297).

21561455 is an equidigital number, since it uses as much as digits as its factorization.

21561455 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4312296.

The product of its digits is 6000, while the sum is 29.

The square root of 21561455 is about 4643.4313820708. The cubic root of 21561455 is about 278.3295739350.

Adding to 21561455 its reverse (55416512), we get a palindrome (76977967).

The spelling of 21561455 in words is "twenty-one million, five hundred sixty-one thousand, four hundred fifty-five".