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 A045797 Evenish numbers (prime to 10 and 10's digit is even). 14
 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)
 OFFSET 1,2 COMMENTS From Jianing Song, Apr 27 2019: (Start) 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 LINKS Reinhard Zumkeller, Table of n, a(n) for n = 1..10000 Index entries for linear recurrences with constant coefficients, signature (1,0,0,1,-1). FORMULA 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 a(n) = 5n + O(1). - Charles R Greathouse IV, Jan 09 2023 MATHEMATICA Flatten[Table[10n+{1, 3, 7, 9}, {n, 0, 30, 2}]] (* Harvey P. Dale, Dec 05 2012 *) PROG (Haskell) a045797 n = a045797_list !! (n-1) a045797_list = filter (even . (`mod` 10) . (`div` 10)) a045572_list -- Reinhard Zumkeller, Dec 10 2011 (PARI) is(n)=gcd(n, 10)==1 && n\10%2==0 \\ Charles R Greathouse IV, Sep 24 2015 CROSSREFS Complement of A045798 with respect to A045572. Sequence in context: A306124 A096102 A316157 * A118555 A056652 A014959 Adjacent sequences: A045794 A045795 A045796 * A045798 A045799 A045800 KEYWORD nonn,base,easy,nice AUTHOR J. H. Conway EXTENSIONS More terms from Erich Friedman Offset changed by Reinhard Zumkeller, Dec 10 2011 STATUS approved

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Last modified February 29 16:27 EST 2024. Contains 370425 sequences. (Running on oeis4.)