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A230997 Number of years after which it is possible to have a date falling on same day of the week, but the entire year does not have the same calendar, in the Gregorian calendar. 2
5, 7, 33, 35, 61, 63, 89, 91, 117, 131, 145, 159, 173, 187, 213, 227, 241, 255, 269, 283, 309, 311, 337, 339, 365, 367, 393, 395, 405, 407, 433, 435, 461, 463, 489, 491, 517, 531, 545, 559, 573, 587, 613, 627, 641, 655, 669, 683, 709, 711, 737, 739, 765, 767, 793, 795 (list; graph; refs; listen; history; text; internal format)
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 400.

These are the terms of A230995 not in A230996.

LINKS

Table of n, a(n) for n=1..56.

Time And Date, Repeating Calendar

Time And Date, Gregorian Calendar

EXAMPLE

5 belongs to this sequence because January 1, 2012 falls on same day as January 1, 2017 but the calendar is not completely the same for both the years. In fact, a difference of 5 years can never produce the same calendar for the entire year.

7 belongs to this sequence because January 1, 2097 falls on same day as January 1, 2104 but the calendar is not completely the same for both the years. In fact, a difference of 7 years can never produce the same calendar for the entire year.

PROG

(PARI) for(i=0, 400, j=0; for(y=0, 400, if(((5*(y\4)+(y%4)-(y\100)+(y\400))%7)==((5*((y+i)\4)+((y+i)%4)-((y+i)\100)+((y+i)\400))%7), j=1; break)); for(y=0, 400, if(((5*(y\4)+(y%4)-(y\100)+(y\400))%7)==((5*((y+i)\4)+((y+i)%4)-((y+i)\100)+((y+i)\400))%7)&&((5*(y\4)+(y%4)-(y\100)+(y\400)-!(y%4)+!(y%100)-!(y%400))%7)==((5*((y+i)\4)+((y+i)%4)-((y+i)\100)+((y+i)\400)-!((y+i)%4)+!((y+i)%100)-!((y+i)%400))%7), j=2; break)); if(j==1, print1(i", ")))

CROSSREFS

Cf. A230995-A231014.

Cf. A231002 (Julian calendar).

Sequence in context: A284405 A232237 A104815 * A243019 A007911 A066172

Adjacent sequences:  A230994 A230995 A230996 * A230998 A230999 A231000

KEYWORD

nonn,easy

AUTHOR

Aswini Vaidyanathan, Nov 02 2013

STATUS

approved

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Last modified November 19 00:12 EST 2019. Contains 329310 sequences. (Running on oeis4.)