21287137 has 2 divisors, whose sum is σ = 21287138. Its totient is φ = 21287136.

The previous prime is 21287129. The next prime is 21287143. The reversal of 21287137 is 73178212.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20802721 + 484416 = 4561^2 + 696^2 .

It is a cyclic number.

It is not a de Polignac number, because 21287137 - 2³ = 21287129 is a prime.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 21287099 and 21287108.

It is not a weakly prime, because it can be changed into another prime (21287437) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10643568 + 10643569.

It is an arithmetic number, because the mean of its divisors is an integer number (10643569).

Almost surely, 2^21287137 is an apocalyptic number.

It is an amenable number.

21287137 is a deficient number, since it is larger than the sum of its proper divisors (1).

21287137 is an equidigital number, since it uses as much as digits as its factorization.

21287137 is an evil number, because the sum of its binary digits is even.

The product of its digits is 4704, while the sum is 31.

The square root of 21287137 is about 4613.7985434997. The cubic root of 21287137 is about 277.1441728855.

The spelling of 21287137 in words is "twenty-one million, two hundred eighty-seven thousand, one hundred thirty-seven".