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 A309725 #8 Aug 14 2019 14:28:49
%S A309725 3,5,31,365,6271,129130,2877421,66628441,1578320767,37983592076,
%T A309725 925196176906,22754692780561,564123212097901,14079691134569845,
%U A309725 353428830512017081,8915830309096530865,225890912989184760703,5744976464242932324976,146603288011226858621356
%N A309725 Number of set partitions of {1,2,...,3n} with sizes in {[n, n, n], [2n, n], [3n]}.
%C A309725 Fourth column in A260876. Apart from a(0) the same as A326998.
%Y A309725 Cf. A260876, A260878, A326998.
%K A309725 nonn,easy
%O A309725 0,1
%A A309725 _Peter Luschny_, Aug 14 2019