Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #13 Feb 28 2020 22:10:48
%S 3,1,4,11,5,19,1,6,27,1,2,7,20,43,1,8,51,59,9,67,1,3,1,10,83,29,22,7,
%T 2,11,1,52,107,23,1,12,123,1,2,131,5,4,139,13,1,38,53,2,163,1,14,171,
%U 25,8,179,187,1,2,15,1,100,26,211,5,54,3,1,16,227,77
%N Second factor in happy factorization of n-th rhombic number.
%C a(n) = A007967(A007970(n)) = A007970(n) / A191856(n);
%C (A191856(n), a(n)) is a 2-happy couple;
%C notation: E in the Conway link.
%H Reinhard Zumkeller, <a href="/A191857/b191857.txt">Table of n, a(n) for n = 1..99</a>
%H J. H. Conway, <a href="http://www.cs.uwaterloo.ca/journals/JIS/happy.html">On Happy Factorizations</a>, J. Integer Sequences, Vol. 1, 1998, #1.
%o (Haskell)
%o a191857 = a007967 . a007970 -- _Reinhard Zumkeller_, Oct 11 2015
%Y Cf. A007967, A007970, A191856.
%K nonn
%O 1,1
%A _Reinhard Zumkeller_, Jun 18 2011
%E Wrong formula removed (thanks to _Wolfdieter Lang_, who pointed this out), by _Reinhard Zumkeller_, Oct 11 2015