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
2012 is a term, since only Jan 13 2012, Apr 13 2012 and Jul 13 2012 fell on Fridays.
MATHEMATICA
Module[{mos={#[[1]], Length[#]}&/@(Flatten[Take[#, 1]&/@DateSelect[ DateRange[ {1900, 1, 1}, {2200, 12, 1}], #Day==13&&#DayName== Friday&]]// Split)}, Select[ mos, #[[2]]>2&][[All, 1]]] (* Requires Mathematica version 12 or later *) (* Harvey P. Dale, Jan 17 2021 *)
PROG
(Haskell)
a190653 n = a190653_list !! (n-1)
a190653_list = filter ((== 3) . 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)) == 3
print(list(filter(ok, range(1901, 2193)))) # Michael S. Branicky, Sep 12 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, May 16 2011
STATUS
approved