21561155 has 16 divisors (see below), whose sum is σ = 32258304. Its totient is φ = 13440480.

The previous prime is 21561131. The next prime is 21561167. The reversal of 21561155 is 55116512.

It is not a de Polignac number, because 21561155 - 2⁶ = 21561091 is a prime.

It is a super-3 number, since 3×21561155³ (a number of 23 digits) contains 333 as substring.

It is a Duffinian number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 27617 + ... + 28386.

It is an arithmetic number, because the mean of its divisors is an integer number (2016144).

Almost surely, 2^21561155 is an apocalyptic number.

21561155 is a deficient number, since it is larger than the sum of its proper divisors (10697149).

21561155 is a wasteful number, since it uses less digits than its factorization.

21561155 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 56026.

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

The square root of 21561155 is about 4643.3990782615. The cubic root of 21561155 is about 278.3282830626.

Adding to 21561155 its reverse (55116512), we get a palindrome (76677667).

The spelling of 21561155 in words is "twenty-one million, five hundred sixty-one thousand, one hundred fifty-five".