A009188 Short leg of more than one Pythagorean triangle.

9, 12, 15, 16, 18, 20, 21, 24, 25, 27, 28, 30, 32, 33, 35, 36, 39, 40, 42, 44, 45, 48, 49, 50, 51, 52, 54, 55, 56, 57, 60, 63, 64, 65, 66, 68, 69, 70, 72, 75, 76, 77, 78, 80, 81, 84, 85, 87, 88, 90, 91, 92, 93, 95, 96, 98, 99, 100, 102, 104, 105, 108, 110, 111, 112, 114, 115, 116

Offset

1,1

Comments

Values of n for which composite n X n magic squares are possible. - J. Lowell, May 20 2010

If n is in the sequence, k*n is in the sequence for all k > 1. So odd semiprimes (A046315) and numbers of the form 4*p where p is an odd prime are core subsequences which give the initial terms of arithmetic progressions in this sequence. - Altug Alkan, Nov 29 2015

Numbers appearing more than once in A009004. - Sean A. Irvine, Apr 20 2018

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Maple

filter:= proc(n) not isprime(n) and (n::odd or not isprime(n/2)) end proc:
select(filter, [$9 .. 10000]); # Robert Israel, Nov 30 2015

Mathematica

filterQ[n_] := !PrimeQ[n] && (OddQ[n] || !PrimeQ[n/2]);
Select[Range[9, 120], filterQ] (* Jean-François Alcover, Feb 28 2019, from Maple *)

Prog

(PARI) forcomposite(n=9, 1e3, if(n % 2 == 1 || !isprime(n/2), print1(n, ", "))) \\ Altug Alkan, Dec 01 2015

Crossrefs

Cf. A001749, A009004, A020884, A046315, A264828.

Sequence in context: A336754 A336756 A114306 * A138299 A050435 A176656

Adjacent sequences: A009185 A009186 A009187 * A009189 A009190 A009191

Keyword

nonn

Author

David W. Wilson

Status

approved