21255780 has 192 divisors, whose sum is σ = 77898240. Its totient is φ = 4202496.

The previous prime is 21255761. The next prime is 21255791. The reversal of 21255780 is 8755212.

21255780 = T₇₇₆ + T₇₇₇ + ... + T₈₄₀.

It is a Harshad number since it is a multiple of its sum of digits (30).

It is an unprimeable number.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 92706 + ... + 92934.

It is an arithmetic number, because the mean of its divisors is an integer number (405720).

Almost surely, 2^21255780 is an apocalyptic number.

21255780 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 21255780, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (38949120).

21255780 is an abundant number, since it is smaller than the sum of its proper divisors (56642460).

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

21255780 is a wasteful number, since it uses less digits than its factorization.

21255780 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 278 (or 276 counting only the distinct ones).

The product of its (nonzero) digits is 5600, while the sum is 30.

The square root of 21255780 is about 4610.3991150442. The cubic root of 21255780 is about 277.0080236786.

The spelling of 21255780 in words is "twenty-one million, two hundred fifty-five thousand, seven hundred eighty".