21678145 has 32 divisors (see below), whose sum is σ = 29998080. Its totient is φ = 14929920.

The previous prime is 21678143. The next prime is 21678161. The reversal of 21678145 is 54187612.

It is not a de Polignac number, because 21678145 - 2¹ = 21678143 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a self number, because there is not a number n which added to its sum of digits gives 21678145.

It is not an unprimeable number, because it can be changed into a prime (21678143) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 49849 + ... + 50281.

It is an arithmetic number, because the mean of its divisors is an integer number (937440).

Almost surely, 2^21678145 is an apocalyptic number.

21678145 is the 2945-th heptagonal number.

It is an amenable number.

21678145 is a deficient number, since it is larger than the sum of its proper divisors (8319935).

21678145 is a wasteful number, since it uses less digits than its factorization.

21678145 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 505.

The product of its digits is 13440, while the sum is 34.

The square root of 21678145 is about 4655.9794887864. The cubic root of 21678145 is about 278.8307748511.

The spelling of 21678145 in words is "twenty-one million, six hundred seventy-eight thousand, one hundred forty-five".