A392678 - OEIS

%I #32 Mar 01 2026 22:24:14

%S 15,130,654,21114,4598780,245633790,5364544542,200916041330

%N The smallest number k > 1 such that the total number of distinct prime factors of the digital reversal of k, when written in all bases b, where 2 <= b <= n, equals b.

%H Daniel Suteu, <a href="/A392678/a392678.pl.txt">Perl program</a>

%e a(5) = 21114 as 21114_10 = 101001001111010_2 = 1001222000_3 = 11021322_4 = 1133424_5 whose digital reversals are 10111100100101_2 = 12069_10, 2221001_3 = 2134_10, 22312011_4 = 44421_10, 4243311_5 = 71706_10, and the total number of distinct prime factors of 12069, 2134, 44421, 71706 are 2, 3, 4 and 5, respectively.

%o (PARI) isok(k, n) = for (b=2, n, if (omega(fromdigits(Vecrev(digits(k,b)), b)) != b, return(0))); 1;

%o a(n) = my(k=2); while (!isok(k, n), k++); k; \\ _Michel Marcus_, Feb 26 2026

%Y Cf. A393577, A001221, A393263, A393264, A393176.

%K nonn,base,more

%O 2,1

%A _Scott R. Shannon_, Feb 22 2026

%E a(9) from _Daniel Suteu_, Mar 01 2026