21653561 has 2 divisors, whose sum is σ = 21653562. Its totient is φ = 21653560.

The previous prime is 21653549. The next prime is 21653581. The reversal of 21653561 is 16535612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20529961 + 1123600 = 4531^2 + 1060^2 .

It is a cyclic number.

It is not a de Polignac number, because 21653561 - 2⁶ = 21653497 is a prime.

It is a super-3 number, since 3×21653561³ (a number of 23 digits) contains 333 as substring.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21653581) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10826780 + 10826781.

It is an arithmetic number, because the mean of its divisors is an integer number (10826781).

Almost surely, 2^21653561 is an apocalyptic number.

It is an amenable number.

21653561 is a deficient number, since it is larger than the sum of its proper divisors (1).

21653561 is an equidigital number, since it uses as much as digits as its factorization.

21653561 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 5400, while the sum is 29.

The square root of 21653561 is about 4653.3386938842. The cubic root of 21653561 is about 278.7253327324.

The spelling of 21653561 in words is "twenty-one million, six hundred fifty-three thousand, five hundred sixty-one".