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A130334 Smallest m>n such that the m-th and n-th triangular numbers are coprime. 5
2, 4, 10, 6, 7, 10, 9, 10, 13, 12, 13, 22, 15, 16, 22, 18, 19, 22, 21, 22, 25, 24, 25, 37, 27, 28, 37, 30, 31, 37, 33, 34, 37, 36, 37, 46, 39, 40, 46, 42, 43, 46, 45, 46, 52, 48, 49, 58, 51, 52, 58, 54, 55, 58, 57, 58, 61, 60, 61, 73, 63, 64, 73, 66, 67, 70, 69, 70, 73, 72, 73 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

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

Eric Weisstein's World of Mathematics, Triangular Number

Eric Weisstein's World of Mathematics, Relatively Prime

FORMULA

a(n) > n+1 for n>1; a(n) > n+2 for n with n mod 3 = 0;

a(n) = n + A130335(n).

PROG

(Python)

from math import gcd

def A130334(n):

    k, Tn, Tm = n+1, n*(n+1)//2, (n+1)*(n+2)//2

    while gcd(Tn, Tm) != 1:

        k += 1

        Tm += k

    return k # Chai Wah Wu, Sep 16 2021

CROSSREFS

Cf. A000217, A026741, A109007, A130335.

Sequence in context: A135445 A098556 A159585 * A320537 A331708 A227289

Adjacent sequences:  A130331 A130332 A130333 * A130335 A130336 A130337

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, May 28 2007

STATUS

approved

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Last modified October 22 12:48 EDT 2021. Contains 348168 sequences. (Running on oeis4.)