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A065502 Positive numbers divisible by 2 or 5; 1/n not purely periodic after decimal point. 8
2, 4, 5, 6, 8, 10, 12, 14, 15, 16, 18, 20, 22, 24, 25, 26, 28, 30, 32, 34, 35, 36, 38, 40, 42, 44, 45, 46, 48, 50, 52, 54, 55, 56, 58, 60, 62, 64, 65, 66, 68, 70, 72, 74, 75, 76, 78, 80, 82, 84, 85, 86, 88, 90, 92, 94, 95, 96, 98, 100, 102, 104, 105, 106, 108, 110, 112, 114 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

A000035(a(n))*(1-A079998(a(n)))=0; complement of A045572. - Reinhard Zumkeller, Nov 15 2009

Numbers that cannot be prefixed by a single digit to form a prime in decimal representation: A124665 is a subsequence. - Reinhard Zumkeller, Oct 22 2011

Up to 198, this is almost identical to "a(n) = n such that 3^n-1 is not squarefree", with the only exceptions being 39 and 117, which are not in this sequence. Why is that? - Felix Fröhlich, Oct 19 2014

LINKS

Harry J. Smith, Table of n, a(n) for n = 1..1000

Index entries for linear recurrences with constant coefficients, signature (2,-2,2,-2,2,-1).

FORMULA

G.f.: x*(2*x^4+x^2+2) / ((x-1)^2*(x^2-x+1)*(x^2+x+1)). - Colin Barker, Jul 18 2013

a(n) = 10*floor(n/6)+s(n mod 6)-floor(((n-1)mod 6)/5), where s(n) = n+1+floor((n+1)/3). - Gary Detlefs, Oct 05 2013

MAPLE

A065502 := proc(n)

     option remember;

     if n = 1 then

        2;

    else

        for a from procname(n-1)+1 do

            if (a mod 2) =0 or (a mod 5) =0 then

                return a;

            end if;

        end do:

    end if;

end proc; # R. J. Mathar, Jul 20 2012

MATHEMATICA

Select[Range[114], Mod[#, 2] == 0 || Mod[#, 5] == 0 &] (* T. D. Noe, Jul 13 2012 *)

Select[ Range@ 114, MemberQ[{0, 2, 4, 5, 6, 8}, Mod[#, 10]] &] (* Robert G. Wilson v, May 22 2014 *)

PROG

(PARI) { n=0; for (m=1, 10^9, if (m%2 == 0 || m%5 == 0, write("b065502.txt", n++, " ", m); if (n==1000, return)) ) } \\ Harry J. Smith, Oct 20 2009

(Haskell)

a065502 n = a065502_list !! (n-1)

a065502_list = filter ((> 1) . (gcd 10)) [1..]

-- Reinhard Zumkeller, Oct 22 2011

CROSSREFS

Cf. A051628, A047229 (... by 2 or 3).

Sequence in context: A062414 A324694 A249025 * A077255 A262439 A091413

Adjacent sequences:  A065499 A065500 A065501 * A065503 A065504 A065505

KEYWORD

nonn,easy

AUTHOR

Len Smiley, Nov 25 2001

EXTENSIONS

Offset changed from 0 to 1 by Harry J. Smith, Oct 20 2009

STATUS

approved

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Last modified March 21 11:49 EDT 2019. Contains 321368 sequences. (Running on oeis4.)