21978478537 has 2 divisors, whose sum is σ = 21978478538. Its totient is φ = 21978478536.

The previous prime is 21978478523. The next prime is 21978478603. The reversal of 21978478537 is 73587487912.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 15381952576 + 6596525961 = 124024^2 + 81219^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21978478537 is a prime.

It is not a weakly prime, because it can be changed into another prime (21978478507) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10989239268 + 10989239269.

It is an arithmetic number, because the mean of its divisors is an integer number (10989239269).

Almost surely, 2^21978478537 is an apocalyptic number.

It is an amenable number.

21978478537 is a deficient number, since it is larger than the sum of its proper divisors (1).

21978478537 is an equidigital number, since it uses as much as digits as its factorization.

21978478537 is an evil number, because the sum of its binary digits is even.

The product of its digits is 23708160, while the sum is 61.

The spelling of 21978478537 in words is "twenty-one billion, nine hundred seventy-eight million, four hundred seventy-eight thousand, five hundred thirty-seven".