A354547 - OEIS

%I #41 Aug 28 2022 21:12:51

%S 1,2,3,4,5,5,7,8,8,7,11,7,13,14,15,15,17,15,19,14,21,13,23,14,21,26,

%T 14,11,29,21,31,21,33,19,35,21,37,38,39,11,41,35,43,26,11,46,47,11,33,

%U 35,51,17,53,11,39,13,57,31,59,35,61,62,13,35,65,39,67,38

%N Least number k <= n such that sopfr(k) = sopfr(n).

%H Michael De Vlieger, <a href="/A354547/b354547.txt">Table of n, a(n) for n = 1..10000</a>

%e For n = 16 = 2^4, sopfr(16) = 2*4 = 8 and 15 = 3 * 5, sopfr(15)= 3 + 5 = 8 and for k < 15, sopfr(k) != 8, hence a(16) = 15.

%t f[n_] := Plus @@ Times @@@ FactorInteger[n]; f[1] = 0; m = 100; With[{s = Array[f, m]}, Table[FirstPosition[s, s[[n]]][[1]], {n, 1, m}]] (* _Amiram Eldar_, Aug 15 2022 *)

%o (PARI) sopfr(n) = (n=factor(n))[, 1]~*n[, 2]; \\ A001414

%o a(n) = my(s=sopfr(n), k=1); while (sopfr(k) != s, k++); k; \\ _Michel Marcus_, Aug 16 2022

%Y Cf. A001414 (sopfr), A056240, A064364.

%K nonn

%O 1,2

%A _Jean-Marc Rebert_, Aug 15 2022