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A080982 Smallest k such that the k-th triangular number has n^2 as divisor. 4
1, 7, 8, 31, 24, 8, 48, 127, 80, 24, 120, 63, 168, 48, 99, 511, 288, 80, 360, 224, 98, 120, 528, 512, 624, 168, 728, 735, 840, 224, 960, 2047, 242, 288, 49, 1215, 1368, 360, 675, 1024, 1680, 440, 1848, 1088, 324, 528, 2208, 512, 2400, 624, 288, 1183, 2808, 728 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

a(2^k) = 2^(2*k+1)-1; a(m)=m^2-1 and for odd prime powers m;

A080983(n)=A000217(a(n)).

LINKS

Reinhard Zumkeller, Table of n, a(n) for n = 1..1000

PROG

(Haskell)

import Data.List (findIndex)

import Data.Maybe (fromJust)

a080982 n = (+ 1) $ fromJust $

   findIndex ((== 0) . (`mod` (n ^ 2))) $ tail a000217_list

-- Reinhard Zumkeller, Mar 23 2013

CROSSREFS

Cf. A011772.

Sequence in context: A042023 A041102 A136116 * A271901 A042875 A154745

Adjacent sequences:  A080979 A080980 A080981 * A080983 A080984 A080985

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Feb 26 2003

STATUS

approved

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Last modified April 20 17:54 EDT 2019. Contains 322310 sequences. (Running on oeis4.)