21556056437 has 2 divisors, whose sum is σ = 21556056438. Its totient is φ = 21556056436.

The previous prime is 21556056421. The next prime is 21556056461. The reversal of 21556056437 is 73465065512.

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., 19077410641 + 2478645796 = 138121^2 + 49786^2 .

It is a cyclic number.

It is not a de Polignac number, because 21556056437 - 2⁴ = 21556056421 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21556056407) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10778028218 + 10778028219.

It is an arithmetic number, because the mean of its divisors is an integer number (10778028219).

Almost surely, 2^21556056437 is an apocalyptic number.

It is an amenable number.

21556056437 is a deficient number, since it is larger than the sum of its proper divisors (1).

21556056437 is an equidigital number, since it uses as much as digits as its factorization.

21556056437 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 756000, while the sum is 44.

The spelling of 21556056437 in words is "twenty-one billion, five hundred fifty-six million, fifty-six thousand, four hundred thirty-seven".