20556491 has 2 divisors, whose sum is σ = 20556492. Its totient is φ = 20556490.

The previous prime is 20556479. The next prime is 20556493. The reversal of 20556491 is 19465502.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 20556491 - 2²² = 16362187 is a prime.

Together with 20556493, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (20556493) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10278245 + 10278246.

It is an arithmetic number, because the mean of its divisors is an integer number (10278246).

Almost surely, 2^20556491 is an apocalyptic number.

20556491 is a deficient number, since it is larger than the sum of its proper divisors (1).

20556491 is an equidigital number, since it uses as much as digits as its factorization.

20556491 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 10800, while the sum is 32.

The square root of 20556491 is about 4533.9266646032. The cubic root of 20556491 is about 273.9363474781.

The spelling of 20556491 in words is "twenty million, five hundred fifty-six thousand, four hundred ninety-one".