A231236 - OEIS

A231236

Number of years after which it is either not possible to have a date falling on same day of the week, or the entire year can have the same calendar, in the Gregorian calendar.

0, 1, 2, 3, 4, 6, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 34, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 62, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,3

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.

This is the complement of A230997.

LINKS

Table of n, a(n) for n=1..70.

Time And Date, Repeating Calendar

Time And Date, Gregorian Calendar

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, A231236-A231239.

Cf. A231237 (Julian calendar).

Sequence in context: A138561 A376198 A333841 * A346131 A151988 A039255

Adjacent sequences: A231233 A231234 A231235 * A231237 A231238 A231239

KEYWORD

nonn,easy

AUTHOR

Aswini Vaidyanathan, Nov 06 2013

STATUS

approved