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A045803
3-ish numbers (end in 17, 19, 31, 33).
1
17, 19, 31, 33, 117, 119, 131, 133, 217, 219, 231, 233, 317, 319, 331, 333, 417, 419, 431, 433, 517, 519, 531, 533, 617, 619, 631, 633, 717, 719, 731, 733, 817, 819, 831, 833, 917, 919, 931, 933, 1017, 1019, 1031, 1033, 1117, 1119, 1131, 1133, 1217, 1219
OFFSET
1,1
FORMULA
G.f.: x*(17+2*x+12*x^2+2*x^3+67*x^4)/(1-x-x^4+x^5). - Colin Barker, Jan 23 2012
a(n) = -75/2 - (23*(-1)^n)/2 - (9-9*i)*(-i)^n - (9+9*i)*i^n + 25*n where i=sqrt(-1). - Colin Barker, Oct 16 2015
MATHEMATICA
Select[Range[1300], MemberQ[{17, 19, 31, 33}, Mod[#, 100]]&] (* or *) LinearRecurrence[{1, 0, 0, 1, -1}, {17, 19, 31, 33, 117}, 50] (* Harvey P. Dale, Dec 17 2014 *)
PROG
(Haskell)
import Data.List (findIndices)
a045803 n = a045803_list !! (n-1)
a045803_list = findIndices (`elem` [17, 19, 31, 33]) $ cycle [0..99]
-- Reinhard Zumkeller, Jan 23 2012
(PARI) a(n) = -75/2 - (23*(-1)^n)/2 - (9-9*I)*(-I)^n - (9+9*I)*I^n + 25*n \\ Colin Barker, Oct 16 2015
(PARI) Vec(x*(17+2*x+12*x^2+2*x^3+67*x^4)/(1-x-x^4+x^5) + O(x^100)) \\ Colin Barker, Oct 16 2015
CROSSREFS
KEYWORD
nonn,base,easy
AUTHOR
EXTENSIONS
More terms from Erich Friedman
STATUS
approved