21987737 has 2 divisors, whose sum is σ = 21987738. Its totient is φ = 21987736.

The previous prime is 21987727. The next prime is 21987787. The reversal of 21987737 is 73778912.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 18524416 + 3463321 = 4304^2 + 1861^2 .

It is a cyclic number.

It is not a de Polignac number, because 21987737 - 2¹² = 21983641 is a prime.

It is not a weakly prime, because it can be changed into another prime (21987727) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10993868 + 10993869.

It is an arithmetic number, because the mean of its divisors is an integer number (10993869).

Almost surely, 2^21987737 is an apocalyptic number.

It is an amenable number.

21987737 is a deficient number, since it is larger than the sum of its proper divisors (1).

21987737 is an equidigital number, since it uses as much as digits as its factorization.

21987737 is an evil number, because the sum of its binary digits is even.

The product of its digits is 148176, while the sum is 44.

The square root of 21987737 is about 4689.1083374134. The cubic root of 21987737 is about 280.1518606493.

The spelling of 21987737 in words is "twenty-one million, nine hundred eighty-seven thousand, seven hundred thirty-seven".