21661145 has 16 divisors (see below), whose sum is σ = 30025728. Its totient is φ = 14826240.

The previous prime is 21661141. The next prime is 21661151. The reversal of 21661145 is 54116612.

It is not a de Polignac number, because 21661145 - 2² = 21661141 is a prime.

It is a super-2 number, since 2×21661145² = 938410405422050, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21661141) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 10649 + ... + 12518.

It is an arithmetic number, because the mean of its divisors is an integer number (1876608).

Almost surely, 2^21661145 is an apocalyptic number.

It is an amenable number.

21661145 is a deficient number, since it is larger than the sum of its proper divisors (8364583).

21661145 is a wasteful number, since it uses less digits than its factorization.

21661145 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 23200.

The product of its digits is 1440, while the sum is 26.

The square root of 21661145 is about 4654.1535213184. The cubic root of 21661145 is about 278.7578694314.

Adding to 21661145 its reverse (54116612), we get a palindrome (75777757).

It can be divided in two parts, 21 and 661145, that added together give a palindrome (661166).

The spelling of 21661145 in words is "twenty-one million, six hundred sixty-one thousand, one hundred forty-five".