21775780 has 48 divisors (see below), whose sum is σ = 50090544. Its totient is φ = 7902720.

The previous prime is 21775777. The next prime is 21775783. The reversal of 21775780 is 8757712.

It is an interprime number because it is at equal distance from previous prime (21775777) and next prime (21775783).

It can be written as a sum of positive squares in 8 ways, for example, as 1127844 + 20647936 = 1062^2 + 4544^2 .

It is not an unprimeable number, because it can be changed into a prime (21775783) 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, 15174 + ... + 16546.

It is an arithmetic number, because the mean of its divisors is an integer number (1043553).

Almost surely, 2^21775780 is an apocalyptic number.

21775780 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 21775780, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25045272).

21775780 is an abundant number, since it is smaller than the sum of its proper divisors (28314764).

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

21775780 is a wasteful number, since it uses less digits than its factorization.

21775780 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1456 (or 1454 counting only the distinct ones).

The product of its (nonzero) digits is 27440, while the sum is 37.

The square root of 21775780 is about 4666.4526141385. The cubic root of 21775780 is about 279.2487514862.

The spelling of 21775780 in words is "twenty-one million, seven hundred seventy-five thousand, seven hundred eighty".