# Greetings from The On-Line Encyclopedia of Integer Sequences! http://oeis.org/ Search: id:a083390 Showing 1-1 of 1 %I A083390 #19 Jan 22 2023 13:53:27 %S A083390 7,10,16,17,19,22,25,27,28,31,32,34,37,38,42,43,45,46,47,49,52,55,57, %T A083390 58,59,61,64,66,67,70,71,72,73,76,77,79,80,82,85,87,88,91,92,93,94,97, %U A083390 100,101,102,103,104,106,107,108,109,110,112,115,117,118,122,123,124,126 %N A083390 m such that 2m + 1 divides lcm(1,3,5,...,2m - 1). %C A083390 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 A083390 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 A083390 Harvey P. Dale, Table of n, a(n) for n = 1..2500 %F A083390 a(n) = (A061346(n)-1)/2. - _David Wasserman_, Oct 26 2004 %e A083390 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 A083390 Select[Range[150],Divisible[LCM@@Range[1,2#-1,2],2#+1]&] (* _Harvey P. Dale_, Jan 22 2023 *) %o A083390 (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 A083390 Cf. A080765. %K A083390 nonn %O A083390 1,1 %A A083390 _Lekraj Beedassy_, Jun 11 2003 %E A083390 More terms from _David Wasserman_, Oct 26 2004 # Content is available under The OEIS End-User License Agreement: http://oeis.org/LICENSE