A231009 Number of months after which it is not possible to have the same calendar for the entire month with the same number of days, in the Gregorian calendar.

1, 2, 4, 5, 7, 10, 11, 12, 13, 16, 19, 21, 24, 25, 27, 28, 30, 33, 36, 39, 42, 44, 45, 47, 48, 51, 53, 56, 59, 61, 62, 65, 70, 71, 73, 74, 79, 82, 83, 85, 88, 91, 93, 96, 97, 99, 100, 102, 105, 108, 111, 116, 119, 120, 125, 128, 131, 133, 134, 137, 139, 142, 143, 145, 146, 148

Offset

1,2

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 A231006.

Links

Table of n, a(n) for n=1..66.

Time And Date, Repeating Months

Time And Date, Gregorian Calendar

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]&&x[(q%4800)+1]==x[((q+p)%4800)+1], j=1; break)); if(j==0, print1(p", ")))

Crossrefs

Cf. A230995-A231014.

Cf. A231014 (Julian calendar).

Sequence in context: A296344 A060565 A231014 * A133254 A080725 A182337

Adjacent sequences: A231006 A231007 A231008 * A231010 A231011 A231012

Keyword

nonn,easy

Author

Aswini Vaidyanathan, Nov 02 2013

Status

approved