21651616 has 48 divisors (see below), whose sum is σ = 49097664. Its totient is φ = 9206784.

The previous prime is 21651607. The next prime is 21651667. The reversal of 21651616 is 61615612.

It is a super-2 number, since 2×21651616² = 937584950822912, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (28).

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 36216 + ... + 36808.

It is an arithmetic number, because the mean of its divisors is an integer number (1022868).

Almost surely, 2^21651616 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21651616, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24548832).

21651616 is an abundant number, since it is smaller than the sum of its proper divisors (27446048).

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

21651616 is a wasteful number, since it uses less digits than its factorization.

21651616 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 773 (or 765 counting only the distinct ones).

The product of its digits is 2160, while the sum is 28.

The square root of 21651616 is about 4653.1296994604. The cubic root of 21651616 is about 278.7169871151.

The spelling of 21651616 in words is "twenty-one million, six hundred fifty-one thousand, six hundred sixteen".