21161555 has 8 divisors (see below), whose sum is σ = 25419744. Its totient is φ = 16912000.

The previous prime is 21161551. The next prime is 21161557. The reversal of 21161555 is 55516112.

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

It is not a de Polignac number, because 21161555 - 2² = 21161551 is a prime.

It is a super-2 number, since 2×21161555² = 895622820036050, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21161551) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 6155 + ... + 8955.

It is an arithmetic number, because the mean of its divisors is an integer number (3177468).

Almost surely, 2^21161555 is an apocalyptic number.

21161555 is a deficient number, since it is larger than the sum of its proper divisors (4258189).

21161555 is a wasteful number, since it uses less digits than its factorization.

21161555 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4317.

The product of its digits is 1500, while the sum is 26.

The square root of 21161555 is about 4600.1690186340. The cubic root of 21161555 is about 276.5980999743.

Adding to 21161555 its reverse (55516112), we get a palindrome (76677667).

The spelling of 21161555 in words is "twenty-one million, one hundred sixty-one thousand, five hundred fifty-five".