21513780 has 72 divisors (see below), whose sum is σ = 66673152. Its totient is φ = 5612736.

The previous prime is 21513773. The next prime is 21513787. The reversal of 21513780 is 8731512.

It is an interprime number because it is at equal distance from previous prime (21513773) and next prime (21513787).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21513787) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 7189 + ... + 9731.

It is an arithmetic number, because the mean of its divisors is an integer number (926016).

Almost surely, 2^21513780 is an apocalyptic number.

21513780 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 21513780, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (33336576).

21513780 is an abundant number, since it is smaller than the sum of its proper divisors (45159372).

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

21513780 is a wasteful number, since it uses less digits than its factorization.

21513780 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2605 (or 2600 counting only the distinct ones).

The product of its (nonzero) digits is 1680, while the sum is 27.

The square root of 21513780 is about 4638.2949453436. The cubic root of 21513780 is about 278.1242823699.

The spelling of 21513780 in words is "twenty-one million, five hundred thirteen thousand, seven hundred eighty".