21355969 has 2 divisors, whose sum is σ = 21355970. Its totient is φ = 21355968.

The previous prime is 21355967. The next prime is 21355987. The reversal of 21355969 is 96955312.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 11992369 + 9363600 = 3463^2 + 3060^2 .

It is a cyclic number.

It is not a de Polignac number, because 21355969 - 2¹ = 21355967 is a prime.

It is a super-2 number, since 2×21355969² = 912154823857922, which contains 22 as substring.

Together with 21355967, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (21355963) 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, 10677984 + 10677985.

It is an arithmetic number, because the mean of its divisors is an integer number (10677985).

Almost surely, 2^21355969 is an apocalyptic number.

It is an amenable number.

21355969 is a deficient number, since it is larger than the sum of its proper divisors (1).

21355969 is an equidigital number, since it uses as much as digits as its factorization.

21355969 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 72900, while the sum is 40.

The square root of 21355969 is about 4621.2518866645. The cubic root of 21355969 is about 277.4425669091.

The spelling of 21355969 in words is "twenty-one million, three hundred fifty-five thousand, nine hundred sixty-nine".