21011720281 has 16 divisors (see below), whose sum is σ = 21434356944. Its totient is φ = 20594294784.

The previous prime is 21011720267. The next prime is 21011720381. The reversal of 21011720281 is 18202711012.

It is a happy number.

It can be written as a sum of positive squares in 8 ways, for example, as 5912225881 + 15099494400 = 76891^2 + 122880^2 .

It is a cyclic number.

It is not a de Polignac number, because 21011720281 - 2⁷ = 21011720153 is a prime.

It is a super-2 number, since 2×21011720281² (a number of 21 digits) contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21011720381) 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, 4359585 + ... + 4364401.

It is an arithmetic number, because the mean of its divisors is an integer number (1339647309).

Almost surely, 2^21011720281 is an apocalyptic number.

It is an amenable number.

21011720281 is a deficient number, since it is larger than the sum of its proper divisors (422636663).

21011720281 is a wasteful number, since it uses less digits than its factorization.

21011720281 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5340.

The product of its (nonzero) digits is 448, while the sum is 25.

The spelling of 21011720281 in words is "twenty-one billion, eleven million, seven hundred twenty thousand, two hundred eighty-one".