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A225881 Numbers k that are equal to the product of the largest triangular proper divisor of k and the sum of all triangular proper divisors of k. 3
285, 5016, 24021, 142350, 145665, 154602, 204450, 318912, 474192, 843402, 1196690, 1283664, 1670250, 2739021, 3412950, 4255776, 5052135, 6054880, 6272140, 6433440, 6493728, 6650712, 6728190, 7156044, 7323030, 7797750, 9379350, 10108840, 10188864 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

A triangular proper divisor of k is a positive triangular number less than k that divides k. - N. J. A. Sloane, Jul 04 2021

LINKS

Donovan Johnson, Table of n, a(n) for n = 1..300

EXAMPLE

5016 = 66*(66+6+3+1).

MATHEMATICA

pltQ[n_]:=Module[{d=Select[Divisors[n], OddQ[Sqrt[1+8#]]&]}, n == Total[ d] Last[d]]; Select[Range[2, 205000], pltQ] (* The program generates the first 7 terms of the sequence. To generate more, increase the Range constant. *) (* Harvey P. Dale, Jul 03 2021 *)

PROG

(PARI)

msumprop(n)={k=1; i=1; s=0; d=1; while(k<=n\2, if(n/k==n\k, d=k; s+=d); i+=1; k+=i); s*=d; return(s)}

{for (n=2, 10^7, if(n==msumprop(n), print(n)))}

CROSSREFS

Cf. A000217, A225880, A225882.

Sequence in context: A105921 A209311 A176712 * A332919 A278629 A241970

Adjacent sequences:  A225878 A225879 A225880 * A225882 A225883 A225884

KEYWORD

nonn

AUTHOR

Antonio Roldán, May 19 2013

STATUS

approved

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Last modified January 28 06:43 EST 2022. Contains 350654 sequences. (Running on oeis4.)