25556891978 has 4 divisors (see below), whose sum is σ = 38335337970. Its totient is φ = 12778445988.

The previous prime is 25556891903. The next prime is 25556891981. The reversal of 25556891978 is 87919865552.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in only one way, i.e., 20872447729 + 4684444249 = 144473^2 + 68443^2 .

It is a super-4 number, since 4×25556891978⁴ (a number of 43 digits) contains 4444 as substring.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 6389222993 + ... + 6389222996.

Almost surely, 2^25556891978 is an apocalyptic number.

25556891978 is a deficient number, since it is larger than the sum of its proper divisors (12778445992).

25556891978 is a wasteful number, since it uses less digits than its factorization.

25556891978 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 12778445991.

The product of its digits is 54432000, while the sum is 65.

The spelling of 25556891978 in words is "twenty-five billion, five hundred fifty-six million, eight hundred ninety-one thousand, nine hundred seventy-eight".