21216780 has 72 divisors (see below), whose sum is σ = 69315792. Its totient is φ = 5222016.

The previous prime is 21216773. The next prime is 21216781. The reversal of 21216780 is 8761212.

It is not an unprimeable number, because it can be changed into a prime (21216781) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 2194 + ... + 6873.

Almost surely, 2^21216780 is an apocalyptic number.

21216780 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21216780 is an abundant number, since it is smaller than the sum of its proper divisors (48099012).

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

21216780 is a wasteful number, since it uses less digits than its factorization.

21216780 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9095 (or 9090 counting only the distinct ones).

The product of its (nonzero) digits is 1344, while the sum is 27.

The square root of 21216780 is about 4606.1676044191. The cubic root of 21216780 is about 276.8385023067.

Adding to 21216780 its reverse (8761212), we get a palindrome (29977992).

The spelling of 21216780 in words is "twenty-one million, two hundred sixteen thousand, seven hundred eighty".