21651786 has 96 divisors (see below), whose sum is σ = 55036800. Its totient is φ = 6329664.

The previous prime is 21651781. The next prime is 21651793. The reversal of 21651786 is 68715612.

It is a self number, because there is not a number n which added to its sum of digits gives 21651786.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21651781) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 145240 + ... + 145388.

It is an arithmetic number, because the mean of its divisors is an integer number (573300).

Almost surely, 2^21651786 is an apocalyptic number.

21651786 is a gapful number since it is divisible by the number (26) formed by its first and last digit.

It is a practical number, because each smaller number is the sum of distinct divisors of 21651786, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27518400).

21651786 is an abundant number, since it is smaller than the sum of its proper divisors (33385014).

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

21651786 is a wasteful number, since it uses less digits than its factorization.

21651786 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 202 (or 190 counting only the distinct ones).

The product of its digits is 20160, while the sum is 36.

The square root of 21651786 is about 4653.1479666995. The cubic root of 21651786 is about 278.7177165720.

The spelling of 21651786 in words is "twenty-one million, six hundred fifty-one thousand, seven hundred eighty-six".