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A231008
Number of months after which it is not possible to have a date falling on the same day of the week, in the Gregorian calendar.
1
2, 4, 5, 7, 10, 12, 13, 16, 21, 24, 25, 30, 33, 36, 39, 42, 47, 48, 51, 56, 59, 62, 65, 79, 82, 85, 88, 93, 96, 97, 102, 105, 108, 111, 119, 120, 128, 134, 137, 139, 142, 148, 151, 154, 156, 157, 165, 168, 174, 180, 183, 188, 191, 192, 194, 197, 200, 211, 214, 220, 228, 229
OFFSET
1,1
COMMENTS
In the Gregorian calendar, a non-century year is a leap year if and only if it is a multiple of 4 and a century year is a leap year if and only if it is a multiple of 400.
Assuming this fact, this sequence is periodic with a period of 4800.
This is the complement of A231005.
PROG
(PARI) m=[0, 3, 3, 6, 1, 4, 6, 2, 5, 0, 3, 5]; n=[31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]; y=vector(4800, i, (m[((i-1)%12)+1]+((5*((i-1)\48)+(((i-1)\12)%4)-((i-1)\1200)+((i-1)\4800)-!((i-1)%48)+!((i-1)%1200)-!((i-1)%4800)-!((i-2)%48)+!((i-2)%1200)-!((i-2)%4800))))%7); x=vector(4800, i, n[((i-1)%12)+1]+!((i-2)%48)-!((i-2)%1200)+!((i-2)%4800)); for(p=0, 4800, j=0; for(q=0, 4800, if(y[(q%4800)+1]==y[((q+p)%4800)+1], j=1; break)); if(j==0, print1(p", ")))
CROSSREFS
Cf. A231013 (Julian calendar).
Sequence in context: A285251 A325124 A231013 * A092311 A335365 A186386
KEYWORD
nonn,easy
AUTHOR
Aswini Vaidyanathan, Nov 02 2013
STATUS
approved