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A231238 Number of months after which either it is not possible to have a date to fall on the same day of the week, or that it is possible to have a date falling on the same day of the week and the two months have the same number of days, in the Gregorian calendar. 1
0, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 13, 14, 15, 16, 17, 18, 20, 21, 22, 23, 24, 25, 26, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 46, 47, 48, 49, 50, 51, 52, 54, 55, 56, 57, 58, 59, 60, 62, 63, 64, 65, 66, 67, 68, 69, 72, 75, 76, 77, 78, 79, 80, 81, 82, 84, 85, 86, 87 (list; graph; refs; listen; history; text; internal format)
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 A231007.

LINKS

Table of n, a(n) for n=1..74.

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], j=1; break)); for(q=0, 4800, if(y[(q%4800)+1]==y[((q+p)%4800)+1]&&x[(q%4800)+1]==x[((q+p)%4800)+1], j=2; break)); if(j!=1, print1(p", ")))

CROSSREFS

Cf. A230995-A231014, A231236-A231239.

Cf. A231239 (Julian calendar).

Sequence in context: A333501 A247801 A004775 * A231239 A328869 A004744

Adjacent sequences:  A231235 A231236 A231237 * A231239 A231240 A231241

KEYWORD

nonn,easy

AUTHOR

Aswini Vaidyanathan, Nov 06 2013

STATUS

approved

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Last modified May 27 21:52 EDT 2020. Contains 334671 sequences. (Running on oeis4.)