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A175850 Numbers m with property that m-th triangular number is a sum of divisors of some n-th triangular number (A175849). 2
1, 13, 12, 384, 575, 783, 4095, 4607, 4095, 6912, 12543, 13824, 16895, 21504, 20735, 27264, 40959, 68256, 76544, 104832, 175104, 130559, 146432, 180224, 129024, 202239, 316224, 328320, 372735, 395199, 333291, 512000, 384463, 532575, 439206 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..35.

Zak Seidov, Table of values of n, m

Zak Seidov, A175849,A175850

FORMULA

sigma(T(n))=T(m); A000203(A000217(n))=A000217(m).

EXAMPLE

Some pairs of n,m:

1,1; 8,13; 9,12; 215,384; 458,575; 520,783; 2232,4095; 3251,4607; 3634,4095; 5349,6912; 9489,12543; 10051,13824.

PROG

(PARI) {for(n=1, 10^7, m=sigma(n*(n+1)/2); issquare(d=1+8*m)&print(n, ", "(sqrtint(d)-1)/2))}

CROSSREFS

Cf. A000203 sigma(n) = sum of divisors of n, A000217 Triangular numbers, A175849 Corresponding values of n.

Sequence in context: A113548 A249998 A195210 * A176306 A291368 A051392

Adjacent sequences:  A175847 A175848 A175849 * A175851 A175852 A175853

KEYWORD

nonn

AUTHOR

Zak Seidov, Sep 27 2010

STATUS

approved

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Last modified October 13 20:38 EDT 2019. Contains 327981 sequences. (Running on oeis4.)