20991427 has 2 divisors, whose sum is σ = 20991428. Its totient is φ = 20991426.

The previous prime is 20991403. The next prime is 20991431. The reversal of 20991427 is 72419902.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20991427 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 20991392 and 20991401.

It is not a weakly prime, because it can be changed into another prime (20991437) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10495713 + 10495714.

It is an arithmetic number, because the mean of its divisors is an integer number (10495714).

Almost surely, 2^20991427 is an apocalyptic number.

20991427 is a deficient number, since it is larger than the sum of its proper divisors (1).

20991427 is an equidigital number, since it uses as much as digits as its factorization.

20991427 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 9072, while the sum is 34.

The square root of 20991427 is about 4581.6402084843. The cubic root of 20991427 is about 275.8548692631.

The spelling of 20991427 in words is "twenty million, nine hundred ninety-one thousand, four hundred twenty-seven".