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A116048 sigma(n) times the n-th prime gives a triangular number. 0
5, 7, 15, 96 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
Probably finite.
No further terms up to n = 1 million. - Harvey P. Dale, Apr 15 2018
LINKS
EXAMPLE
prime(5) * sigma(5) = 11 * 6 = T(12).
prime(7) * sigma(7) = 17 * 8 = T(18).
prime(15) * sigma(15) = 47 * 24 = T(48).
prime(96) * sigma(96) = 503 * 252 = T(503).
MATHEMATICA
Select[Range[200], OddQ[Sqrt[8(Prime[#]DivisorSigma[1, #])+1]]&] (* Harvey P. Dale, Apr 15 2018 *)
PROG
(PARI) isok(n) = ispolygonal(sigma(n)*prime(n), 3); \\ Michel Marcus, Jul 05 2014
CROSSREFS
Sequence in context: A067589 A059613 A242503 * A120282 A132094 A082878
KEYWORD
nonn
AUTHOR
Giovanni Resta, Feb 13 2006
STATUS
approved

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Last modified February 26 09:21 EST 2024. Contains 370338 sequences. (Running on oeis4.)