21351972672 has 168 divisors, whose sum is σ = 64647348480. Its totient is φ = 6727311360.

The previous prime is 21351972667. The next prime is 21351972683. The reversal of 21351972672 is 27627915312.

It is a happy number.

21351972672 is a `hidden beast` number, since 2 + 1 + 3 + 519 + 72 + 67 + 2 = 666.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 753904 + ... + 781712.

Almost surely, 2^21351972672 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 21351972672, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32323674240).

21351972672 is an abundant number, since it is smaller than the sum of its proper divisors (43295375808).

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

21351972672 is a wasteful number, since it uses less digits than its factorization.

21351972672 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 27901 (or 27888 counting only the distinct ones).

The product of its digits is 317520, while the sum is 45.

The spelling of 21351972672 in words is "twenty-one billion, three hundred fifty-one million, nine hundred seventy-two thousand, six hundred seventy-two".