20718421 has 2 divisors, whose sum is σ = 20718422. Its totient is φ = 20718420.

The previous prime is 20718419. The next prime is 20718431. The reversal of 20718421 is 12481702.

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., 20376196 + 342225 = 4514^2 + 585^2 .

It is a cyclic number.

It is not a de Polignac number, because 20718421 - 2¹ = 20718419 is a prime.

Together with 20718419, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20718431) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10359210 + 10359211.

It is an arithmetic number, because the mean of its divisors is an integer number (10359211).

Almost surely, 2^20718421 is an apocalyptic number.

It is an amenable number.

20718421 is a deficient number, since it is larger than the sum of its proper divisors (1).

20718421 is an equidigital number, since it uses as much as digits as its factorization.

20718421 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 896, while the sum is 25.

The square root of 20718421 is about 4551.7492241994. The cubic root of 20718421 is about 274.6537614969.

It can be divided in two parts, 20718 and 421, that multiplied together give a palindrome (8722278).

The spelling of 20718421 in words is "twenty million, seven hundred eighteen thousand, four hundred twenty-one".