21561629 has 2 divisors, whose sum is σ = 21561630. Its totient is φ = 21561628.

The previous prime is 21561607. The next prime is 21561697. The reversal of 21561629 is 92616512.

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., 20748025 + 813604 = 4555^2 + 902^2 .

It is a cyclic number.

It is not a de Polignac number, because 21561629 - 2¹⁶ = 21496093 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21561595 and 21561604.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21561329) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10780814 + 10780815.

It is an arithmetic number, because the mean of its divisors is an integer number (10780815).

Almost surely, 2^21561629 is an apocalyptic number.

It is an amenable number.

21561629 is a deficient number, since it is larger than the sum of its proper divisors (1).

21561629 is an equidigital number, since it uses as much as digits as its factorization.

21561629 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 6480, while the sum is 32.

The square root of 21561629 is about 4643.4501181772. The cubic root of 21561629 is about 278.3303226355.

The spelling of 21561629 in words is "twenty-one million, five hundred sixty-one thousand, six hundred twenty-nine".