OFFSET
1,2
COMMENTS
LINKS
G. C. Greubel, Table of n, a(n) for n = 1..5000
EXAMPLE
sopfr(21) = sum of primes dividing 21 (with repetition) = 10, which is the 4th triangular number, so 21 is in this sequence.
The number 1 is here because the sum of its prime factors is 0, which is a triangular number.
MATHEMATICA
triangularQ[n_] := IntegerQ[Sqrt[1 + 8*n]]; fQ[n_] := Module[{p, e}, {p, e} = Transpose[FactorInteger[n]]; triangularQ[Dot[p, e]]]; Join[{1}, Select[Range[2, 500], fQ]] (* T. D. Noe, May 30 2012 *)
PROG
(PARI) sopfr(n) = my(f=factor(n)); sum(k=1, matsize(f)[1], f[k, 1]*f[k, 2]); \\ A001414
isok(n) = ispolygonal(sopfr(n), 3); \\ Michel Marcus, May 02 2018
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Jonathan Vos Post, May 28 2012
STATUS
approved