21072780 has 36 divisors (see below), whose sum is σ = 63921312. Its totient is φ = 5619360.

The previous prime is 21072769. The next prime is 21072823. The reversal of 21072780 is 8727012.

It is a tau number, because it is divible by the number of its divisors (36).

It is a hoax number, since the sum of its digits (27) coincides with the sum of the digits of its distinct prime factors.

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 58356 + ... + 58715.

It is an arithmetic number, because the mean of its divisors is an integer number (1775592).

Almost surely, 2^21072780 is an apocalyptic number.

21072780 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21072780 is an abundant number, since it is smaller than the sum of its proper divisors (42848532).

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

21072780 is a wasteful number, since it uses less digits than its factorization.

21072780 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 117086 (or 117081 counting only the distinct ones).

The product of its (nonzero) digits is 1568, while the sum is 27.

The square root of 21072780 is about 4590.5097756132. The cubic root of 21072780 is about 276.2107715773.

Adding to 21072780 its reverse (8727012), we get a palindrome (29799792).

The spelling of 21072780 in words is "twenty-one million, seventy-two thousand, seven hundred eighty".