81551438 has 4 divisors (see below), whose sum is σ = 122327160. Its totient is φ = 40775718.

The previous prime is 81551429. The next prime is 81551443. The reversal of 81551438 is 83415518.

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

It is a junction number, because it is equal to n+sod(n) for n = 81551398 and 81551407.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 20387858 + ... + 20387861.

It is an arithmetic number, because the mean of its divisors is an integer number (30581790).

Almost surely, 2^81551438 is an apocalyptic number.

81551438 is a deficient number, since it is larger than the sum of its proper divisors (40775722).

81551438 is a wasteful number, since it uses less digits than its factorization.

81551438 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 40775721.

The product of its digits is 19200, while the sum is 35.

The square root of 81551438 is about 9030.5834805953. The cubic root of 81551438 is about 433.6545170431.

The spelling of 81551438 in words is "eighty-one million, five hundred fifty-one thousand, four hundred thirty-eight".