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A045797
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Evenish numbers (prime to 10 and 10's digit is even).
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14
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1, 3, 7, 9, 21, 23, 27, 29, 41, 43, 47, 49, 61, 63, 67, 69, 81, 83, 87, 89, 101, 103, 107, 109, 121, 123, 127, 129, 141, 143, 147, 149, 161, 163, 167, 169, 181, 183, 187, 189, 201, 203, 207, 209, 221, 223, 227, 229, 241, 243, 247, 249, 261, 263, 267, 269, 281
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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1,2
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COMMENTS
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Numbers congruent to {1, 3, 7, 9} mod 20.
Numbers k such that Kronecker(-20,k) = A289741(k) = +1. (End)
First 20 terms are congruences of 3^k mod 100. - Dario Vuksan, Jan 09 2023
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LINKS
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FORMULA
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Conjecture a(n) = a(n-1)+a(n-4)-a(n-5). G.f.: x*(1+2*x+4*x^2+2*x^3+11*x^4) / ((1-x)^2*(1+x)*(1+x^2)). - Colin Barker, Apr 14 2012
The conjecture above is correct. - Jianing Song, Apr 27 2019
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MATHEMATICA
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Flatten[Table[10n+{1, 3, 7, 9}, {n, 0, 30, 2}]] (* Harvey P. Dale, Dec 05 2012 *)
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PROG
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(Haskell)
a045797 n = a045797_list !! (n-1)
a045797_list = filter (even . (`mod` 10) . (`div` 10)) a045572_list
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CROSSREFS
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KEYWORD
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nonn,base,easy,nice
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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