21356549 has 2 divisors, whose sum is σ = 21356550. Its totient is φ = 21356548.

The previous prime is 21356507. The next prime is 21356563. The reversal of 21356549 is 94565312.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21325924 + 30625 = 4618^2 + 175^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21356549 is a prime.

It is a super-2 number, since 2×21356549² = 912204370378802, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21356579) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10678274 + 10678275.

It is an arithmetic number, because the mean of its divisors is an integer number (10678275).

Almost surely, 2^21356549 is an apocalyptic number.

It is an amenable number.

21356549 is a deficient number, since it is larger than the sum of its proper divisors (1).

21356549 is an equidigital number, since it uses as much as digits as its factorization.

21356549 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 32400, while the sum is 35.

The square root of 21356549 is about 4621.3146397968. The cubic root of 21356549 is about 277.4450785447.

The spelling of 21356549 in words is "twenty-one million, three hundred fifty-six thousand, five hundred forty-nine".