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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
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
KEYWORD
nonn,base,easy,nice
AUTHOR
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.)