A354547 Least number k <= n such that sopfr(k) = sopfr(n).

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, 14, 11, 29, 21, 31, 21, 33, 19, 35, 21, 37, 38, 39, 11, 41, 35, 43, 26, 11, 46, 47, 11, 33, 35, 51, 17, 53, 11, 39, 13, 57, 31, 59, 35, 61, 62, 13, 35, 65, 39, 67, 38

Offset: 1

Author

Jean-Marc Rebert, Aug 15 2022

Keywords

• nonn

Examples

			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.
		

Links

• Michael De Vlieger, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A001414 (sopfr), A056240, A064364.

Programs

Mathematica

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 *)

PARI

sopfr(n) = (n=factor(n))[, 1]~*n[, 2]; \\ A001414
a(n) = my(s=sopfr(n), k=1); while (sopfr(k) != s, k++); k; \\ Michel Marcus, Aug 16 2022