21405155 has 8 divisors (see below), whose sum is σ = 25711152. Its totient is φ = 17107488.

The previous prime is 21405149. The next prime is 21405169. The reversal of 21405155 is 55150412.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21405155 - 2⁸ = 21404899 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21405155.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 8189 + ... + 10481.

It is an arithmetic number, because the mean of its divisors is an integer number (3213894).

Almost surely, 2^21405155 is an apocalyptic number.

21405155 is a deficient number, since it is larger than the sum of its proper divisors (4305997).

21405155 is a wasteful number, since it uses less digits than its factorization.

21405155 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4165.

The product of its (nonzero) digits is 1000, while the sum is 23.

The square root of 21405155 is about 4626.5705441504. The cubic root of 21405155 is about 277.6554008791.

Adding to 21405155 its reverse (55150412), we get a palindrome (76555567).

The spelling of 21405155 in words is "twenty-one million, four hundred five thousand, one hundred fifty-five".