21405376381 has 2 divisors, whose sum is σ = 21405376382. Its totient is φ = 21405376380.

The previous prime is 21405376331. The next prime is 21405376411. The reversal of 21405376381 is 18367350412.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19636416900 + 1768959481 = 140130^2 + 42059^2 .

It is a cyclic number.

It is not a de Polignac number, because 21405376381 - 2⁷ = 21405376253 is a prime.

It is a super-2 number, since 2×21405376381² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21405376331) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10702688190 + 10702688191.

It is an arithmetic number, because the mean of its divisors is an integer number (10702688191).

Almost surely, 2^21405376381 is an apocalyptic number.

It is an amenable number.

21405376381 is a deficient number, since it is larger than the sum of its proper divisors (1).

21405376381 is an equidigital number, since it uses as much as digits as its factorization.

21405376381 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 120960, while the sum is 40.

The spelling of 21405376381 in words is "twenty-one billion, four hundred five million, three hundred seventy-six thousand, three hundred eighty-one".