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A215011 a(n) = least k>0 such that triangular(n) divides Fibonacci(k). 3
1, 4, 12, 15, 20, 8, 24, 12, 60, 10, 60, 84, 56, 40, 60, 18, 36, 36, 90, 120, 40, 120, 24, 300, 175, 252, 72, 168, 140, 60, 60, 60, 180, 360, 120, 228, 342, 252, 420, 60, 40, 88, 660, 60, 120, 48, 48, 168, 1400, 900, 252, 189, 108, 180, 120, 72, 252, 406, 1740 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Triangular(n)=n*(n+1)/2 is the n-th triangular number.

LINKS

Table of n, a(n) for n=1..59.

EXAMPLE

Triangular(2)=3, least k>0 such that 3 divides Fibonacci(k) is k=4, so a(2)=4.

PROG

(Python)

TOP = 333

prpr = y = 0

prev = k = 1

res = [-1]*TOP

while y<TOP-1:

    for i in range(1, TOP):

      if res[i]<0 and prev % (i*(i+1)/2) == 0:

        res[i] = k

        y += 1

    curr = prpr+prev

    prpr = prev

    prev = curr

    k += 1

for i in range(1, TOP):

    print res[i],

CROSSREFS

Cf. A085779 (least k such that triangular(n) divides k!).

Cf. A001177 (least k such that n divides Fibonacci(k)).

Cf. A132632 (least k such that n^2 divides Fibonacci(k)).

Cf. A132633 (least k such that n^3 divides Fibonacci(k)).

Cf. A215453 (least k such that n^n divides Fibonacci(k)).

Cf. A214528 (least k such that n! divides Fibonacci(k)).

Cf. A000217, A000045.

Sequence in context: A260257 A256706 A103020 * A024353 A024354 A020883

Adjacent sequences:  A215008 A215009 A215010 * A215012 A215013 A215014

KEYWORD

nonn

AUTHOR

Alex Ratushnyak, Aug 08 2012

STATUS

approved

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Last modified November 15 11:35 EST 2018. Contains 317238 sequences. (Running on oeis4.)