A393263 The smallest number k > 1 such that the total number of its distinct prime factors equals that of the digit reversals of k when it is written in all bases 2 to n.

3, 5, 5, 7, 7, 13, 13, 13, 13, 13, 13, 178, 178, 178, 1452823, 1861487, 4181923, 4181923, 4181923, 783468688, 783468688, 783468688

Offset

2,1

Links

Table of n, a(n) for n=2..23.

Example

a(7) = 13 as the total number of distinct prime factors of 13 is 1, while with digital reversals of 13 in base 2, 3, 4, 5, 6, 7 are 11, 13, 7, 17, 8, 43 respectively, all of which have one distinct prime factor. No smaller number satisfies this criterion.

Prog

(PARI) isok(k, n) = my(v=vector(n-1, b, omega(fromdigits(Vecrev(digits(k, b+1)), b+1)))); (#Set(v) == 1) && (v[1] == omega(k));
a(n) = my(k=2); while(!isok(k, n), k++); k; \\ Michel Marcus, Feb 16 2026

Crossrefs

Cf. A001221, A393264, A393176.

Sequence in context: A088081 A387853 A206768 * A168322 A396962 A393264

Adjacent sequences: A393260 A393261 A393262 * A393264 A393265 A393266

Keyword

nonn,base,more

Author

Scott R. Shannon, Feb 07 2026

Status

approved