21651678 has 64 divisors (see below), whose sum is σ = 51840000. Its totient is φ = 6676992.

The previous prime is 21651667. The next prime is 21651683. The reversal of 21651678 is 87615612.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 47998 + ... + 48446.

It is an arithmetic number, because the mean of its divisors is an integer number (810000).

Almost surely, 2^21651678 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21651678, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25920000).

21651678 is an abundant number, since it is smaller than the sum of its proper divisors (30188322).

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

21651678 is a wasteful number, since it uses less digits than its factorization.

21651678 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 526 (or 520 counting only the distinct ones).

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

The square root of 21651678 is about 4653.1363616382. The cubic root of 21651678 is about 278.7172531527.

The spelling of 21651678 in words is "twenty-one million, six hundred fifty-one thousand, six hundred seventy-eight".