21694381 has 2 divisors, whose sum is σ = 21694382. Its totient is φ = 21694380.

The previous prime is 21694367. The next prime is 21694391. The reversal of 21694381 is 18349612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19980900 + 1713481 = 4470^2 + 1309^2 .

It is a cyclic number.

It is not a de Polignac number, because 21694381 - 2²¹ = 19597229 is a prime.

It is a super-2 number, since 2×21694381² = 941292333946322, which contains 22 as substring.

It is an alternating number because its digits alternate between even and odd.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21694301) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10847190 + 10847191.

It is an arithmetic number, because the mean of its divisors is an integer number (10847191).

Almost surely, 2^21694381 is an apocalyptic number.

It is an amenable number.

21694381 is a deficient number, since it is larger than the sum of its proper divisors (1).

21694381 is an equidigital number, since it uses as much as digits as its factorization.

21694381 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 10368, while the sum is 34.

The square root of 21694381 is about 4657.7227268269. The cubic root of 21694381 is about 278.9003682400.

The spelling of 21694381 in words is "twenty-one million, six hundred ninety-four thousand, three hundred eighty-one".