Properties of the Number 391

Three Hundred Ninety-One

Basics

Value: 390 → 391 → 392

Parity: odd

Prime: No

Previous Prime: 389

Next Prime: 397

Digit Sum: 13

Digital Root: 4

Palindrome: No

Factorization: 17 × 23

Divisors: 1, 17, 23, 391

Polygonal

Triangular: No

Square: No

Pentagonal: No

Hexagonal: No

Heptagonal: No

Tetrahedral: No

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Representations

Binary: 110000111

Octal: 607

Duodecimal: 287

Hexadecimal: 187

Square: 152881

Square Root: 19.77371993328519

Classification

Fibonacci: No

Bell Number: No

Factorial Number: No

Regular Number: No

Perfect Number: No

Special

Kaprekar Constant: No

Munchausen Constant: No

Armstrong Number: No

Kaprekar Number: No

Catalan Number: No

Vampire Number: No

Taxicab Number: No

Super Prime: No

Friedman Number: No

Fermat Number: No

Cullen Number: No

OEIS Sequences

a(n) = 2·n² - 1. A56220

Centered pentagonal numbers: (5n²+5n+2)/2; crystal ball sequence for 3.3.3.4.4. planar net. A5891

Smith (or joke) numbers: composite numbers k such that sum of digits of k = sum of digits of prime factors of k (counted with multiplicity). A6753

Brilliant numbers: semiprimes (products of two primes, A001358) whose prime factors have the same number of decimal digits. A78972

Prime shift array: Square array read by antidiagonals: A(1,col) = 2·col, and for row > 1, A(row,col) = A003961(A(row-1,col)). A246278

Sieve of Eratosthenes arranged as an array and read by antidiagonals as A(1,1), A(1,2), A(2,1), A(1,3), A(2,2), A(3,1), ... A83221

Number of permutations p of [n] satisfying i-2 <= p(i) <= i+4 for all i in [n]. A72850

a(n) = 10·n + 1. A17281

Number of partitions of n into parts >= 3. A8483

Nonprime numbers k such that binomial(k+p,k) mod k = 1, where p=10. A133630