

A009188


Short leg of more than one Pythagorean triangle.


5



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
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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] (* JeanFrançois 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: A170951 A044859 A114306 * A138299 A050435 A176656
Adjacent sequences: A009185 A009186 A009187 * A009189 A009190 A009191


KEYWORD

nonn


AUTHOR

David W. Wilson


STATUS

approved



