21123506212656 has 80 divisors (see below), whose sum is σ = 54625941216000. Its totient is φ = 7033831339264.

The previous prime is 21123506212649. The next prime is 21123506212657. The reversal of 21123506212656 is 65621260532112.

It is a super-2 number, since 2×21123506212656² (a number of 27 digits) contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21123506212657) 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, 307579090 + ... + 307647758.

It is an arithmetic number, because the mean of its divisors is an integer number (682824265200).

Almost surely, 2^{21123506212656} is an apocalyptic number.

It is an amenable number.

21123506212656 is an abundant number, since it is smaller than the sum of its proper divisors (33502435003344).

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

21123506212656 is a wasteful number, since it uses less digits than its factorization.

21123506212656 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 75266 (or 75260 counting only the distinct ones).

The product of its (nonzero) digits is 259200, while the sum is 42.

Adding to 21123506212656 its reverse (65621260532112), we get a palindrome (86744766744768).

The spelling of 21123506212656 in words is "twenty-one trillion, one hundred twenty-three billion, five hundred six million, two hundred twelve thousand, six hundred fifty-six".