OFFSET
1,1
LINKS
Reinhard Zumkeller, Table of n, a(n) for n = 1..1000
Eric Weisstein's World of Mathematics, Triskaidekaphobia
Wikipedia, Triskaidekaphobia
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
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, May 16 2011
STATUS
approved