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A053670 Least number coprime to n and n+1. 14
3, 5, 5, 3, 7, 5, 3, 5, 7, 3, 5, 5, 3, 11, 7, 3, 5, 5, 3, 11, 5, 3, 5, 7, 3, 5, 5, 3, 7, 7, 3, 5, 5, 3, 11, 5, 3, 5, 7, 3, 5, 5, 3, 7, 7, 3, 5, 5, 3, 7, 5, 3, 5, 7, 3, 5, 5, 3, 7, 7, 3, 5, 5, 3, 7, 5, 3, 5, 11, 3, 5, 5, 3, 7, 7, 3, 5, 5, 3, 7, 5, 3, 5, 11, 3, 5, 5, 3, 7, 11, 3, 5, 5, 3, 7, 5, 3, 5, 7, 3, 5 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

A179675(n) = smallest m such that a(m) = n-th odd prime. - Reinhard Zumkeller, Jul 23 2010

LINKS

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

MATHEMATICA

a[n_] := For[k = 3, True, k++, If[CoprimeQ[k, n, n+1], Return[k]]]; Table[a[n], {n, 1, 101}] (* Jean-Fran├žois Alcover, Sep 20 2012 *)

PROG

(Haskell)

a053670 n = head [x | x <- [3, 5 ..],

                      n `gcd` x == 1, (n + 1) `gcd` x == 1]

-- Reinhard Zumkeller, Dec 28 2012

(PARI) a(n)=my(N=n*(n+1), k=2); while(gcd(k++, N)>1, ); k \\ Charles R Greathouse IV, Nov 10 2015

(Python)

from math import gcd

def a(n):

    k, m = 3, n*(n+1)

    while gcd(k, m) != 1: k += 2

    return k

print([a(n) for n in range(1, 102)]) # Michael S. Branicky, Sep 25 2021

CROSSREFS

Cf. A053669-A053674.

Sequence in context: A129488 A211023 A279494 * A085963 A282177 A184593

Adjacent sequences:  A053667 A053668 A053669 * A053671 A053672 A053673

KEYWORD

nonn,nice,easy

AUTHOR

Henry Bottomley, Feb 15 2000

EXTENSIONS

More terms from Andrew Gacek (andrew(AT)dgi.net), Feb 21 2000 and James A. Sellers, Feb 22 2000

STATUS

approved

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Last modified July 4 07:52 EDT 2022. Contains 355068 sequences. (Running on oeis4.)