A084372 Least composite k such that the nearest integer to the average of the smallest and largest prime factors of k equals n.

4, 6, 10, 14, 35, 22, 26, 65, 34, 38, 95, 46, 115, 161, 58, 62, 155, 217, 74, 185, 82, 86, 215, 94, 235, 329, 106, 265, 371, 118, 122, 305, 427, 134, 335, 142, 146, 365, 511, 158, 395, 166, 415, 581, 178, 445, 623, 1501, 194, 485, 202, 206, 515, 214, 218, 545, 226

Offset

2,1

Comments

"Nearest integer" here rounds half-integers up. - Robert Israel, Sep 22 2025

Links

Robert Israel, Table of n, a(n) for n = 2..10000

Formula

If n is in A098090, then a(n) = 2*(2*n-3), otherwise a(n) = A020481(2*n) * (2*n - A020481(2*n)). - Robert Israel, Sep 22 2025

Maple

f:= proc(n) local p;
  if isprime(2*n-3) then return (2*(2*n-3)) fi;
  p:= 2:
  do
    p:= nextprime(p); if isprime(2*n-p) then return p*(2*n-p) fi
  od
end proc:
f(2):= 4:
map(f, [$2..100]); # Robert Israel, Sep 22 2025

Crossrefs

Cf. A076690, A020481, A098090.

Sequence in context: A061645 A188592 A188586 * A353543 A388014 A388971

Adjacent sequences: A084369 A084370 A084371 * A084373 A084374 A084375

Keyword

nonn,look

Author

Jason Earls, Jun 23 2003

Status

approved