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 A190651 #16 Feb 16 2025 08:33:14
%S A190651 1902,1904,1909,1910,1913,1915,1916,1919,1921,1924,1926,1927,1930,
%T A190651 1932,1937,1938,1941,1943,1944,1947,1949,1952,1954,1955,1958,1960,
%U A190651 1965,1966,1969,1971,1972,1975,1977,1980,1982,1983,1986,1988,1993,1994,1997,1999,2000
%N A190651 Years with exactly one "Friday the 13th", starting from 1901.
%H A190651 Reinhard Zumkeller, <a href="/A190651/b190651.txt">Table of n, a(n) for n = 1..1000</a>
%H A190651 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Triskaidekaphobia.html">Triskaidekaphobia</a>
%H A190651 Wikipedia, <a href="http://en.wikipedia.org/wiki/Triskaidekaphobia">Triskaidekaphobia</a>
%H A190651 <a href="/index/Ca#calendar">Index entries for sequences related to calendars</a>
%F A190651 A101312(a(n)) = 1, 1 <= A101312(n) <= 3.
%e A190651 1902 is a term, since only Jun 13 1902 fell on a Friday.
%t A190651 Select[Range[1901,2001],Count[Table[DayName@{#,m,13},{m,12}],Friday]==1&] (* _Giorgos Kalogeropoulos_, Sep 12 2021 *)
%o A190651 (Haskell)
%o A190651 a190651 n = a190651_list !! (n-1)
%o A190651 a190651_list = filter ((== 1) . a101312) [1901..]
%o A190651 (Python)
%o A190651 from datetime import date
%o A190651 def ok(n): return sum(date.isoweekday(date(n, m, 13)) == 5 for m in range(1, 13)) == 1
%o A190651 print(list(filter(ok, range(1901, 2001)))) # _Michael S. Branicky_, Sep 12 2021
%Y A190651 Cf. A101312, A190652, A190653.
%K A190651 nonn
%O A190651 1,1
%A A190651 _Reinhard Zumkeller_, May 16 2011