21011720381 has 2 divisors, whose sum is σ = 21011720382. Its totient is φ = 21011720380.

The previous prime is 21011720267. The next prime is 21011720383. The reversal of 21011720381 is 18302711012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20946772900 + 64947481 = 144730^2 + 8059^2 .

It is a cyclic number.

It is not a de Polignac number, because 21011720381 - 2³⁴ = 3831851197 is a prime.

It is a super-2 number, since 2×21011720381² (a number of 21 digits) contains 22 as substring.

Together with 21011720383, it forms a pair of twin primes.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21011720381.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21011720383) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10505860190 + 10505860191.

It is an arithmetic number, because the mean of its divisors is an integer number (10505860191).

Almost surely, 2^21011720381 is an apocalyptic number.

It is an amenable number.

21011720381 is a deficient number, since it is larger than the sum of its proper divisors (1).

21011720381 is an equidigital number, since it uses as much as digits as its factorization.

21011720381 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 672, while the sum is 26.

The spelling of 21011720381 in words is "twenty-one billion, eleven million, seven hundred twenty thousand, three hundred eighty-one".