A329026 Numbers k such that k = Product(p_j^e_j) = concatenation(pi(p_j)), where pi = A000720.

12, 14, 2127, 1232495490

Offset

1,1

Comments

Numbers k such that k equals concatenation of indices of distinct prime factors of k, in increasing order.

Fixed points of A329025.

No other terms below 10^17. - Max Alekseyev, Feb 21 2025

Links

Table of n, a(n) for n=1..4.

Index entries for sequences computed from indices in prime factorization

Example

2127 is a term because 2127 = 3 * 709 = prime(2) * prime(127) = concat(2, 127).

Mathematica

a[n_] := FromDigits[Flatten@IntegerDigits@(PrimePi[#[[1]]] & /@ FactorInteger[n])]; Select[Range[2200], a[#] == # &]

Crossrefs

Cf. A000720, A329025.

Sequence in context: A318298 A139310 A221819 * A307535 A180575 A115402

Adjacent sequences: A329023 A329024 A329025 * A329027 A329028 A329029

Keyword

nonn,base,more

Author

Ilya Gutkovskiy, Nov 02 2019

Extensions

a(4) from Giovanni Resta, Nov 04 2019

Status

approved