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A184549
Super-birthdays (falling on the same weekday), version 1 (birth within the year following a February 29).
4
0, 6, 17, 23, 28, 34, 45, 51, 56, 62, 73, 79, 84, 90, 101, 107, 112, 118, 129, 135, 140, 146, 157, 163, 168, 174, 185, 191, 196, 202, 213, 219, 224, 230, 241, 247, 252, 258, 269, 275, 280, 286, 297, 303, 308, 314
OFFSET
0,2
COMMENTS
See example and the link for more explanation and limits of validity.
The offset is motivated by the special status of the initial term a(0)=0.
REFERENCES
Alexandre Moatti, Récréations mathéphysiques, Editions le Pommier. ISBN: 9782746504875.
LINKS
Charles R Greathouse IV, Re: Super-birthdays, seqfan list, Jan 2011.
FORMULA
a(n) = a(n-1)+a(n-4)-a(n-5). G.f.: x*(5*x^3+6*x^2+11*x+6) / ((x-1)^2*(x+1)*(x^2+1)). - Colin Barker, Nov 04 2013
EXAMPLE
A standard year has 365 = 350+14+1 = 1 (mod 7) days,
and a leap year has 366 = 2 (mod 7) days.
A super-birthday occurs when this sums up to a multiple of 7.
If you are born in the year following a Feb 29:
1+1+1+2+1+1 = 7 after 6 years,
1+2+1+1+1+2+1+1 +1+2+1 = 14, 11 years later, i.e. age of 17,
1+1+2+1+1+1 = 7, 6 years later: age of 23,
2+1+1+1+2 = 7, 5 years later: age of 28,
and then the same cycles repeat.
MATHEMATICA
LinearRecurrence[{1, 0, 0, 1, -1}, {0, 6, 17, 23, 28}, 100] (* Paolo Xausa, Mar 17 2024 *)
PROG
(PARI) a(n)=[0, 6, 17, 23][n%4+1]+n\4*28
(PARI) Vec(x*(5*x^3+6*x^2+11*x+6)/((x-1)^2*(x+1)*(x^2+1)) + O(x^100)) \\ Colin Barker, Nov 04 2013
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Eric Angelini and M. F. Hasler, Jan 16 2011
STATUS
approved