login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A190652 Years with exactly two "Friday the 13ths", starting from 1901. 4
1901, 1905, 1906, 1907, 1908, 1911, 1912, 1917, 1918, 1920, 1922, 1923, 1929, 1933, 1934, 1935, 1936, 1939, 1940, 1945, 1946, 1948, 1950, 1951, 1957, 1961, 1962, 1963, 1964, 1967, 1968, 1973, 1974, 1976, 1978, 1979, 1985, 1989, 1990, 1991, 1992, 1995, 1996 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
Eric Weisstein's World of Mathematics, Triskaidekaphobia
FORMULA
A101312(a(n)) = 2, 1 <= A101312(n) <= 3.
EXAMPLE
2004 is a term, since only Feb 13 2004 and Aug 13 2004 fell on a Friday.
MATHEMATICA
Select[Range[1901, 2020], Count[Table[{#, m, 13}, {m, 12}], _?(DayName[#] == Friday&)] == 2&] (* Harvey P. Dale, Oct 02 2018 *)
PROG
(Haskell)
a190652 n = a190652_list !! (n-1)
a190652_list = filter ((== 2) . 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)) == 2
print(list(filter(ok, range(1901, 2000)))) # Michael S. Branicky, Sep 12 2021
CROSSREFS
Sequence in context: A204479 A251346 A078862 * A177137 A273913 A190651
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, May 16 2011
STATUS
approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified March 28 05:02 EDT 2024. Contains 371235 sequences. (Running on oeis4.)