21242780 has 24 divisors (see below), whose sum is σ = 48041952. Its totient is φ = 7843392.

The previous prime is 21242759. The next prime is 21242783. The reversal of 21242780 is 8724212.

It is a Harshad number since it is a multiple of its sum of digits (26).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21242783) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 40592 + ... + 41111.

It is an arithmetic number, because the mean of its divisors is an integer number (2001748).

Almost surely, 2^21242780 is an apocalyptic number.

21242780 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21242780 is an abundant number, since it is smaller than the sum of its proper divisors (26799172).

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

21242780 is a wasteful number, since it uses less digits than its factorization.

21242780 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 81725 (or 81723 counting only the distinct ones).

The product of its (nonzero) digits is 1792, while the sum is 26.

The square root of 21242780 is about 4608.9890431634. The cubic root of 21242780 is about 276.9515396116.

Adding to 21242780 its reverse (8724212), we get a palindrome (29966992).

It can be divided in two parts, 21242 and 780, that added together give a palindrome (22022).

The spelling of 21242780 in words is "twenty-one million, two hundred forty-two thousand, seven hundred eighty".