21561737 has 2 divisors, whose sum is σ = 21561738. Its totient is φ = 21561736.

The previous prime is 21561733. The next prime is 21561769. The reversal of 21561737 is 73716512.

It is an a-pointer prime, because the next prime (21561769) can be obtained adding 21561737 to its sum of digits (32).

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21335161 + 226576 = 4619^2 + 476^2 .

It is a cyclic number.

It is not a de Polignac number, because 21561737 - 2² = 21561733 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21561733) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10780868 + 10780869.

It is an arithmetic number, because the mean of its divisors is an integer number (10780869).

Almost surely, 2^21561737 is an apocalyptic number.

It is an amenable number.

21561737 is a deficient number, since it is larger than the sum of its proper divisors (1).

21561737 is an equidigital number, since it uses as much as digits as its factorization.

21561737 is an evil number, because the sum of its binary digits is even.

The product of its digits is 8820, while the sum is 32.

The square root of 21561737 is about 4643.4617474466. The cubic root of 21561737 is about 278.3307873441.

The spelling of 21561737 in words is "twenty-one million, five hundred sixty-one thousand, seven hundred thirty-seven".