21561733 has 2 divisors, whose sum is σ = 21561734. Its totient is φ = 21561732.

The previous prime is 21561697. The next prime is 21561737. The reversal of 21561733 is 33716512.

21561733 is nontrivially palindromic in base 4.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20994724 + 567009 = 4582^2 + 753^2 .

It is a cyclic number.

It is not a de Polignac number, because 21561733 - 2²¹ = 19464581 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21561737) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10780866 + 10780867.

It is an arithmetic number, because the mean of its divisors is an integer number (10780867).

Almost surely, 2^21561733 is an apocalyptic number.

It is an amenable number.

21561733 is a deficient number, since it is larger than the sum of its proper divisors (1).

21561733 is an equidigital number, since it uses as much as digits as its factorization.

21561733 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3780, while the sum is 28.

The square root of 21561733 is about 4643.4613167335. The cubic root of 21561733 is about 278.3307701327.

The spelling of 21561733 in words is "twenty-one million, five hundred sixty-one thousand, seven hundred thirty-three".