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