login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A329026 Numbers k such that k = Product (p_j^e_j) = concatenation (pi(p_j)), where pi = A000720. 1
12, 14, 2127, 1232495490 (list; graph; refs; listen; history; text; internal format)
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.

a(5) > 2.4*10^11, if it exists. - Giovanni Resta, Nov 05 2019

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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified April 6 08:53 EDT 2020. Contains 333268 sequences. (Running on oeis4.)