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A156702
Numbers k such that k^2 - 1 == 0 (mod 24^2).
2
1, 127, 161, 287, 289, 415, 449, 575, 577, 703, 737, 863, 865, 991, 1025, 1151, 1153, 1279, 1313, 1439, 1441, 1567, 1601, 1727, 1729, 1855, 1889, 2015, 2017, 2143, 2177, 2303, 2305, 2431, 2465, 2591, 2593, 2719, 2753, 2879, 2881, 3007, 3041, 3167, 3169
OFFSET
1,2
COMMENTS
Numbers k that are == +-1 (mod 9) and == +-1 (mod 32). - Charles R Greathouse IV, Dec 23 2011
FORMULA
G.f.: (-x^4 + 2*x^3 + 126*x^2 + 34*x + 127)/(x^5 - x^4 - x + 1). - Alexander R. Povolotsky, Feb 15 2009
a(n) = -36 + 27*(-1)^n + (4-4*i)*(-i)^n + (4+4*i)*i^n + 72*n. - Harvey P. Dale, Apr 25 2012
Sum_{n>=1} (-1)^(n+1)/a(n) = (cot(Pi/288) - tan(17*Pi/288))*Pi/288. - Amiram Eldar, Feb 26 2023
E.g.f.: 1 + 8*cos(x) + 9*(8*x - 1)*cosh(x) - 8*sin(x) + 9*(8*x - 7)*sinh(x). - Stefano Spezia, Oct 13 2024
MATHEMATICA
LinearRecurrence[{1, 0, 0, 1, -1}, {1, 127, 161, 287, 289}, 50] (* Vincenzo Librandi, Feb 08 2012 *)
With[{c=24^2}, Select[Range[3200], Divisible[#^2-1, c]&]] (* Harvey P. Dale, Apr 25 2012 *)
PROG
(PARI) a(n)=n\4*288+[-1, 1, 127, 161][n%4+1]
CROSSREFS
Sequence in context: A178088 A006285 A094933 * A180536 A342801 A137985
KEYWORD
nonn,easy
AUTHOR
Vincenzo Librandi, Feb 13 2009
EXTENSIONS
Corrected and edited by Vinay Vaishampayan, Jun 23 2010
STATUS
approved