21861660 has 48 divisors (see below), whose sum is σ = 64816416. Its totient is φ = 5486592.

The previous prime is 21861659. The next prime is 21861667. The reversal of 21861660 is 6616812.

21861660 = 1126² + 1127² + ... + 1142².

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

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21861667) 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, 9697 + ... + 11736.

It is an arithmetic number, because the mean of its divisors is an integer number (1350342).

Almost surely, 2^21861660 is an apocalyptic number.

21861660 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21861660 is an abundant number, since it is smaller than the sum of its proper divisors (42954756).

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

21861660 is a wasteful number, since it uses less digits than its factorization.

21861660 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 21462 (or 21460 counting only the distinct ones).

The product of its (nonzero) digits is 3456, while the sum is 30.

The square root of 21861660 is about 4675.6454099942. The cubic root of 21861660 is about 279.6153732534.

The spelling of 21861660 in words is "twenty-one million, eight hundred sixty-one thousand, six hundred sixty".