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A185027 Sum of the triangular divisors of n. 5
1, 1, 4, 1, 1, 10, 1, 1, 4, 11, 1, 10, 1, 1, 19, 1, 1, 10, 1, 11, 25, 1, 1, 10, 1, 1, 4, 29, 1, 35, 1, 1, 4, 1, 1, 46, 1, 1, 4, 11, 1, 31, 1, 1, 64, 1, 1, 10, 1, 11, 4, 1, 1, 10, 56, 29, 4, 1, 1, 35, 1, 1, 25, 1, 1, 76, 1, 1, 4, 11, 1, 46, 1, 1, 19, 1, 1, 88, 1 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

LINKS

Antonio Roldán, Table of n, a(n) for n = 1..10000

FORMULA

G.f.: Sum_{k>=1} (k*(k + 1)/2)*x^(k*(k+1)/2)/(1 - x^(k*(k+1)/2)). - Ilya Gutkovskiy, Dec 24 2016

EXAMPLE

a(15) = 19 because 1+3+15 = 19 (1, 3 and 15 triangular divisors of 15).

PROG

(PARI)

istriang(x)=issquare(8*x+1)

sumdivtriang(n)=m=0; for(i=1, n, if(istriang(i)&&n/i==n\i, m+=i)); return(m)}

{for(n=1, 10^4, k=sumdivtriang(n); write("b185027.txt", n, " ", k))}

(PARI) a(n)=sumdiv(n, d, ispolygonal(d, 3)*d) \\ Charles R Greathouse IV, Jan 14 2013

CROSSREFS

Cf. A035316.

Sequence in context: A056647 A056057 A226234 * A016520 A109955 A214398

Adjacent sequences:  A185024 A185025 A185026 * A185028 A185029 A185030

KEYWORD

nonn

AUTHOR

Antonio Roldán, Jan 14 2013

STATUS

approved

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Last modified September 21 19:29 EDT 2018. Contains 315260 sequences. (Running on oeis4.)