A392678 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.

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

Offset

2,1

Links

Table of n, a(n) for n=2..9.

Daniel Suteu, Perl program

Example

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.

Prog

(PARI) isok(k, n) = for (b=2, n, if (omega(fromdigits(Vecrev(digits(k, b)), b)) != b, return(0))); 1;
a(n) = my(k=2); while (!isok(k, n), k++); k; \\ Michel Marcus, Feb 26 2026

Crossrefs

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

Sequence in context: A156922 A271791 A155656 * A244878 A275101 A236262

Adjacent sequences: A392675 A392676 A392677 * A392679 A392680 A392681

Keyword

nonn,base,more

Author

Scott R. Shannon, Feb 22 2026

Extensions

a(9) from Daniel Suteu, Mar 01 2026

Status

approved