21780066 has 32 divisors (see below), whose sum is σ = 54309888. Its totient is φ = 5657040.

The previous prime is 21780047. The next prime is 21780067. The reversal of 21780066 is 66008712.

It is a happy number.

It is not an unprimeable number, because it can be changed into a prime (21780067) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 23110 + ... + 24033.

It is an arithmetic number, because the mean of its divisors is an integer number (1697184).

Almost surely, 2^21780066 is an apocalyptic number.

21780066 is an abundant number, since it is smaller than the sum of its proper divisors (32529822).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21780066 is a wasteful number, since it uses less digits than its factorization.

21780066 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 47166.

The product of its (nonzero) digits is 4032, while the sum is 30.

The square root of 21780066 is about 4666.9118268937. The cubic root of 21780066 is about 279.2670712530.

Adding to 21780066 its reverse (66008712), we get a palindrome (87788778).

It can be divided in two parts, 21 and 780066, that added together give a palindrome (780087).

The spelling of 21780066 in words is "twenty-one million, seven hundred eighty thousand, sixty-six".