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A116048
sigma(n) times the n-th prime gives a triangular number.
0
5, 7, 15, 96
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OFFSET
1,1
COMMENTS
Probably finite.
No further terms up to n = 1 million. -
Harvey P. Dale
, Apr 15 2018
LINKS
Table of n, a(n) for n=1..4.
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
Adjacent sequences:
A116045
A116046
A116047
*
A116049
A116050
A116051
KEYWORD
nonn
AUTHOR
Giovanni Resta
, Feb 13 2006
STATUS
approved
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Last modified April 19 07:38 EDT 2024. Contains 371782 sequences. (Running on oeis4.)