A265424 a(n) = ((-1)^n - 1)/2 + 25*floor(3*n/2) - 50*floor(n/4).

0, 24, 75, 99, 100, 124, 175, 199, 200, 224, 275, 299, 300, 324, 375, 399, 400, 424, 475, 499, 500, 524, 575, 599, 600, 624, 675, 699, 700, 724, 775, 799, 800, 824, 875, 899, 900, 924, 975, 999, 1000, 1024, 1075, 1099, 1100, 1124, 1175, 1199, 1200, 1224

Offset

0,2

Comments

Also: solutions to (2a+1)^2 = 1 mod 400. Occurs in the context of a problem concerning integer-valued percentages (see link): a(n) percent of a(n)+1 is an integer.

Links

Table of n, a(n) for n=0..49.

R. Israel, in reply to E. Angelini, Percentages, SeqFan list, Dec 7, 2015.

Formula

a(n) = (A265423(n) - 1)/2.

G.f.: x*(24 + 51*x + 24*x^2 + x^3)/(1 - x - x^4 + x^5). - Robert Israel, Dec 08 2015

Mathematica

Table[((-1)^n - 1)/2 + 25 Floor[3 n/2] - 50 Floor[n/4], {n, 0, 50}] (* Vincenzo Librandi, Dec 09 2015 *)

Prog

(PARI) A265424(n)=((-1)^n-1)/2+n*3\2*25-n\4*50
(PARI) is_A265424(n)=Mod(n*2+1, 400)^2==1
(Magma) [((-1)^n-1)/2+25*Floor(3*n/2)-50*Floor(n/4): n in [0..50]]; // Vincenzo Librandi, Dec 09 2015

Crossrefs

Sequence in context: A042134 A045249 A185940 * A033572 A233883 A291630

Adjacent sequences: A265421 A265422 A265423 * A265425 A265426 A265427

Keyword

nonn,easy

Author

M. F. Hasler, Dec 08 2015

Status

approved