A190651 Years with exactly one "Friday the 13th", starting from 1901.

1902, 1904, 1909, 1910, 1913, 1915, 1916, 1919, 1921, 1924, 1926, 1927, 1930, 1932, 1937, 1938, 1941, 1943, 1944, 1947, 1949, 1952, 1954, 1955, 1958, 1960, 1965, 1966, 1969, 1971, 1972, 1975, 1977, 1980, 1982, 1983, 1986, 1988, 1993, 1994, 1997, 1999, 2000

Offset: 1

Author

Reinhard Zumkeller, May 16 2011

Keywords

• nonn

Examples

			1902 is a term, since only Jun 13 1902 fell on a Friday.
		

Links

• Reinhard Zumkeller, Table of n, a(n) for n = 1..1000
• Eric Weisstein's World of Mathematics, Triskaidekaphobia
• Wikipedia, Triskaidekaphobia
• Index entries for sequences related to calendars

Crossrefs

Cf. A101312, A190652, A190653.

Programs

Haskell

a190651 n = a190651_list !! (n-1)
a190651_list = filter ((== 1) . a101312) [1901..]

Mathematica

Select[Range[1901,2001],Count[Table[DayName@{#,m,13},{m,12}],Friday]==1&] (* Giorgos Kalogeropoulos, Sep 12 2021 *)

Python

from datetime import date
def ok(n): return sum(date.isoweekday(date(n, m, 13)) == 5 for m in range(1, 13)) == 1
print(list(filter(ok, range(1901, 2001)))) # Michael S. Branicky, Sep 12 2021

Formula

A101312(a(n)) = 1, 1 <= A101312(n) <= 3.