This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A173977 #11 Oct 24 2024 03:14:54
%S A173977 5,8,11,13,14,17,20,23,25,26,28,29,32,35,38,41,43,44,46,47,50,53,56,
%T A173977 58,59,62,65,67,68,71,73,74,77,80,83,85,86,88,89,92,95,98,101,103,104,
%U A173977 107,110,113,116,118,119,122,125,127,128,130,131,133,134,137,140,143,146,148
%N A173977 Integers k > 1 for which A020639(2*k-1) < A020639(2*k-3).
%C A173977 Every number m == 2 (mod 3), m > 2, is in the sequence (see A016789).
%p A173977 A020639 := proc(n) if n = 1 then 1; else min(op(numtheory[factorset](n)) ) ; end if; end proc:
%p A173977 isA173977 := proc(n) A020639(2*n-1) < A020639(2*n-3) ; end proc:
%p A173977 for n from 2 to 400 do if isA173977(n) then printf("%d,",n) ; end if; end do: # _R. J. Mathar_, Mar 25 2010
%t A173977 lpf[n_] := lpf[n] = FactorInteger[n][[1, 1]]; Select[Range[2, 150], lpf[2*#-1] < lpf[2*#-3] &] (* _Amiram Eldar_, Oct 24 2024 *)
%Y A173977 Cf. A016789, A020639, A104275.
%K A173977 nonn,easy
%O A173977 1,1
%A A173977 _Vladimir Shevelev_, Mar 04 2010
%E A173977 More terms from _R. J. Mathar_, Mar 25 2010