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

1,1

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

Formula

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

Example

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

Mathematica

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

Prog

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

Crossrefs

Cf. A101312, A190652, A190653.

Sequence in context: A190652 A177137 A273913 * A237787 A190653 A124628

Adjacent sequences: A190648 A190649 A190650 * A190652 A190653 A190654

Keyword

nonn

Author

Reinhard Zumkeller, May 16 2011

Status

approved