21451780 has 48 divisors (see below), whose sum is σ = 52214400. Its totient is φ = 7250688.

The previous prime is 21451769. The next prime is 21451789. The reversal of 21451780 is 8715412.

It is a Harshad number since it is a multiple of its sum of digits (28).

It is not an unprimeable number, because it can be changed into a prime (21451789) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 9171 + ... + 11269.

It is an arithmetic number, because the mean of its divisors is an integer number (1087800).

Almost surely, 2^21451780 is an apocalyptic number.

21451780 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21451780, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26107200).

21451780 is an abundant number, since it is smaller than the sum of its proper divisors (30762620).

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

21451780 is a wasteful number, since it uses less digits than its factorization.

21451780 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2188 (or 2186 counting only the distinct ones).

The product of its (nonzero) digits is 2240, while the sum is 28.

The square root of 21451780 is about 4631.6066326924. The cubic root of 21451780 is about 277.8568522731.

The spelling of 21451780 in words is "twenty-one million, four hundred fifty-one thousand, seven hundred eighty".