21352781 has 2 divisors, whose sum is σ = 21352782. Its totient is φ = 21352780.

The previous prime is 21352733. The next prime is 21352783. The reversal of 21352781 is 18725312.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 16362025 + 4990756 = 4045^2 + 2234^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21352781 is a prime.

It is a super-2 number, since 2×21352781² = 911882512867922, which contains 22 as substring.

Together with 21352783, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21352783) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10676390 + 10676391.

It is an arithmetic number, because the mean of its divisors is an integer number (10676391).

Almost surely, 2^21352781 is an apocalyptic number.

It is an amenable number.

21352781 is a deficient number, since it is larger than the sum of its proper divisors (1).

21352781 is an equidigital number, since it uses as much as digits as its factorization.

21352781 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3360, while the sum is 29.

The square root of 21352781 is about 4620.9069456114. The cubic root of 21352781 is about 277.4287607625.

The spelling of 21352781 in words is "twenty-one million, three hundred fifty-two thousand, seven hundred eighty-one".