%I #19 Jan 22 2023 13:53:27

%S 7,10,16,17,19,22,25,27,28,31,32,34,37,38,42,43,45,46,47,49,52,55,57,

%T 58,59,61,64,66,67,70,71,72,73,76,77,79,80,82,85,87,88,91,92,93,94,97,

%U 100,101,102,103,104,106,107,108,109,110,112,115,117,118,122,123,124,126

%N m such that 2m + 1 divides lcm(1,3,5,...,2m - 1).

%C Also m for which A025547(m)=A025547(m+1). Query: a(n) seems to be equal to A030343(n+4) - 1. Is this true?

%C While any odd number>1 can be the leg of a primitive Pythagorean triangle, the m-th odd number 2m+1=A061346 forms leg common to more than one PPT. - _Lekraj Beedassy_, Jul 12 2006

%H Harvey P. Dale, <a href="/A083390/b083390.txt">Table of n, a(n) for n = 1..2500</a>

%F a(n) = (A061346(n)-1)/2. - _David Wasserman_, Oct 26 2004

%e 10 is in the sequence because we have 2*10 - 1 = 19 and lcm(1,3,5,...,19)=166966608033225=7950790858725*21 which is divisible by 2*10 + 1 = 21.

%t Select[Range[150],Divisible[LCM@@Range[1,2#-1,2],2#+1]&] (* _Harvey P. Dale_, Jan 22 2023 *)

%o (PARI) isok(n) = {lc = 1; for (i = 1, 2*n-1, lc = lcm(lc, i);); return (lc % (2*n+1) == 0);} \\ _Michel Marcus_, Jul 27 2013

%Y Cf. A080765.

%K nonn

%O 1,1

%A _Lekraj Beedassy_, Jun 11 2003

%E More terms from _David Wasserman_, Oct 26 2004