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%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
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