20556391 has 2 divisors, whose sum is σ = 20556392. Its totient is φ = 20556390.

The previous prime is 20556307. The next prime is 20556397. The reversal of 20556391 is 19365502.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 20556391 - 2¹⁵ = 20523623 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20556397) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10278195 + 10278196.

It is an arithmetic number, because the mean of its divisors is an integer number (10278196).

Almost surely, 2^20556391 is an apocalyptic number.

20556391 is the 2868-th centered pentagonal number.

20556391 is a deficient number, since it is larger than the sum of its proper divisors (1).

20556391 is an equidigital number, since it uses as much as digits as its factorization.

20556391 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 8100, while the sum is 31.

The square root of 20556391 is about 4533.9156366214. The cubic root of 20556391 is about 273.9359032765.

The spelling of 20556391 in words is "twenty million, five hundred fifty-six thousand, three hundred ninety-one".