21212521656 has 128 divisors (see below), whose sum is σ = 56204928000. Its totient is φ = 6660588032.

The previous prime is 21212521639. The next prime is 21212521661. The reversal of 21212521656 is 65612521212.

It is an alternating number because its digits alternate between even and odd.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 12724135 + ... + 12725801.

It is an arithmetic number, because the mean of its divisors is an integer number (439101000).

Almost surely, 2^21212521656 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 21212521656, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28102464000).

21212521656 is an abundant number, since it is smaller than the sum of its proper divisors (34992406344).

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

21212521656 is a wasteful number, since it uses less digits than its factorization.

21212521656 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2141 (or 2137 counting only the distinct ones).

The product of its digits is 14400, while the sum is 33.

The spelling of 21212521656 in words is "twenty-one billion, two hundred twelve million, five hundred twenty-one thousand, six hundred fifty-six".