21418237 has 2 divisors, whose sum is σ = 21418238. Its totient is φ = 21418236.

The previous prime is 21418231. The next prime is 21418247. The reversal of 21418237 is 73281412.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 15163236 + 6255001 = 3894^2 + 2501^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21418237 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21418231) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10709118 + 10709119.

It is an arithmetic number, because the mean of its divisors is an integer number (10709119).

Almost surely, 2^21418237 is an apocalyptic number.

It is an amenable number.

21418237 is a deficient number, since it is larger than the sum of its proper divisors (1).

21418237 is an equidigital number, since it uses as much as digits as its factorization.

21418237 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2688, while the sum is 28.

The square root of 21418237 is about 4627.9841183824. The cubic root of 21418237 is about 277.7119534282.

Adding to 21418237 its reverse (73281412), we get a palindrome (94699649).

The spelling of 21418237 in words is "twenty-one million, four hundred eighteen thousand, two hundred thirty-seven".