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 #12 Jan 06 2021 12:45:11
%S 6,9,13,20,31,36,49,54,78,81,117,120,125,169,180,186,201,216,260,279,
%T 294,324,400,403,441,468,486,523,620,637,702,720,729,750,845,961,980,
%U 1014,1053,1080,1116,1125,1206,1296,1366,1519,1521,1560,1620,1625,1674,1764,1809,1944,2197
%N Terms of A176211, duplicates removed.
%C The terms are permanents of a set of certain symmetric (0,1)-matrices as detailed in A176211. Thus the sequence solves a symmetric version of Gristein problem: to find all the values of permanent of all square (0,1) matrices, which contain exactly three 1's in each row and column (see the list of unsolved problems in chapter 8 of Minc's book).
%D H. Minc, Permanents, Addison-Wesley, 1978.
%H V. S. Shevelev, <a href="http://dx.doi.org/10.1007/BF01104103">Some problems of the theory of enumerating the permutations with restricted position</a>, Journal of Soviet Mathematics, 61 (4) (1992) 2272-2317
%o (PARI) f(n) = fibonacci(n+1) + fibonacci(n-1) + 2; \\ A000211
%o lista(nn) = {my(v = vector(nn, k, f(k+2))); my(vmax = vecmax(v)); my(w = vector(nn, k, [0, logint(vmax, v[k])])); my(list=List()); forvec(x = w, if (vecmax(x), my(y = prod(k=1, #v, v[k]^x[k])); if (y <= vmax, listput(list, y)););); Vec(vecsort(list,,8));}
%o lista(14) \\ _Michel Marcus_, Jan 06 2021
%Y Cf. A176211, A176210, A000211.
%K nonn
%O 1,1
%A _Vladimir Shevelev_, Apr 12 2010