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A084967 Multiples of 5 whose GCD's with 6 is 1. 16
5, 25, 35, 55, 65, 85, 95, 115, 125, 145, 155, 175, 185, 205, 215, 235, 245, 265, 275, 295, 305, 325, 335, 355, 365, 385, 395, 415, 425, 445, 455, 475, 485, 505, 515, 535, 545, 565, 575, 595, 605, 625, 635, 655, 665, 685, 695, 715, 725, 745, 755, 775, 785 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Third row of A083140.

Positions of 5 in A020639. - Zak Seidov, Apr 29 2015

LINKS

Table of n, a(n) for n=1..53.

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

FORMULA

Numbers of the form 5k for which GCD(5k, 6) = 1.

a(n) = 5*A007310(n). - Adriano Caroli, Oct 03 2010

a(n) = 5*(-3+(-1)^n+6*n)/2. a(n)=a(n-1)+a(n-2)-a(n-3). G.f.: 5*x*(x^2+4*x+1) / ((x-1)^2*(x+1)). - Colin Barker, Feb 24 2013

lim a(n)/n = A038111(3)/A038110(3) = 15 as n goes to infinity. - Vladimir Shevelev, Jan 20 2015

For n>2, a(n) = a(n-2) + 30. - Zak Seidov, Apr 29 2015

a(n) = A007310(A273669(n)). - Antti Karttunen, May 20 2017

MATHEMATICA

5Select[ Range[160], GCD[ #, 2*3] == 1 & ]

Select[Range[5, 785, 10], Mod[#, 3] > 0 &] (* Zak Seidov, Apr 29 2015 *)

a[1] = 5; a[n_] := a[n] = a[n - 1] + 10*(2 - Mod[n, 2]); Table[a[n], {n, 50}] (* Zak Seidov, Apr 29 2015 *)

PROG

(PARI) is(n)=n%5==0 && gcd(n, 6)==1 \\ Charles R Greathouse IV, Nov 19 2014

(PARI) list(lim)=5*select(k->gcd(n, 6)==1, [1..lim\5]) \\ Charles R Greathouse IV, Nov 19 2014

CROSSREFS

Cf. A083140, A063149, A007310, A273669.

Cf. A020639. - Zak Seidov, Apr 29 2015

Sequence in context: A018639 A029475 A070391 * A249827 A279541 A070390

Adjacent sequences:  A084964 A084965 A084966 * A084968 A084969 A084970

KEYWORD

nonn,easy

AUTHOR

Robert G. Wilson v, Jun 15 2003

STATUS

approved

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Last modified August 17 11:22 EDT 2017. Contains 290635 sequences.