21001523211781 has 8 divisors (see below), whose sum is σ = 24003750936704. Its totient is φ = 17999798017680.

The previous prime is 21001523211751. The next prime is 21001523211829. The reversal of 21001523211781 is 18711232510012.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21001523211781 - 2⁵ = 21001523211749 is a prime.

It is a super-2 number, since 2×21001523211781² (a number of 27 digits) contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21001523211751) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 125543145 + ... + 125710318.

It is an arithmetic number, because the mean of its divisors is an integer number (3000468867088).

Almost surely, 2^{21001523211781} is an apocalyptic number.

It is an amenable number.

21001523211781 is a deficient number, since it is larger than the sum of its proper divisors (3002227724923).

21001523211781 is a wasteful number, since it uses less digits than its factorization.

21001523211781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 251265411.

The product of its (nonzero) digits is 6720, while the sum is 34.

Adding to 21001523211781 its reverse (18711232510012), we get a palindrome (39712755721793).

The spelling of 21001523211781 in words is "twenty-one trillion, one billion, five hundred twenty-three million, two hundred eleven thousand, seven hundred eighty-one".