21211381 has 2 divisors, whose sum is σ = 21211382. Its totient is φ = 21211380.

The previous prime is 21211373. The next prime is 21211387. The reversal of 21211381 is 18311212.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 12006225 + 9205156 = 3465^2 + 3034^2 .

It is a cyclic number.

It is not a de Polignac number, because 21211381 - 2³ = 21211373 is a prime.

It is a super-2 number, since 2×21211381² = 899845367854322, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21211387) 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, 10605690 + 10605691.

It is an arithmetic number, because the mean of its divisors is an integer number (10605691).

Almost surely, 2^21211381 is an apocalyptic number.

It is an amenable number.

21211381 is a deficient number, since it is larger than the sum of its proper divisors (1).

21211381 is an equidigital number, since it uses as much as digits as its factorization.

21211381 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 96, while the sum is 19.

The square root of 21211381 is about 4605.5815050871. The cubic root of 21211381 is about 276.8150180980.

Adding to 21211381 its reverse (18311212), we get a palindrome (39522593).

The spelling of 21211381 in words is "twenty-one million, two hundred eleven thousand, three hundred eighty-one".