A357741 -id:A357741 - cp's OEIS frontend

A106125 Numbers k such that k divides the k-th semiprime.

1, 2, 3, 7, 11, 43, 53, 613367, 613439, 613451, 613523, 613549, 613609, 6384425461, 6384425521, 6384425569, 6384425647

Offset: 1

Shyam Sunder Gupta, May 07 2005

Note that except 1, all other term in the sequence will be primes.

a(18) > 10^12. - Lucas A. Brown, Oct 17 2020

			a(4)=7 is a term because 7 divides the 7th semiprime (i.e., 21).

Lucas A. Brown, semiprimemods.py

Cf. A001358, A356764, A357741.

a(14)-a(17) from Donovan Johnson, Sep 27 2010

A356764 Semiprimes divisible by their indices in the sequence of semiprimes, divided by those indices.

Original entry on oeis.org

4, 3, 3, 3, 3, 3, 3, 5, 5, 5, 5, 5, 5, 7, 7, 7, 7

Offset: 1

Lucas A. Brown, Oct 13 2022

Except for a(1) = 4, all terms are prime.

Lucas A. Brown, semiprimemods.py

Cf. A001358, A106125, A357741.

With[{sp=Select[Range[5*10^6],PrimeOmega[#]==2&]},Select[#[[1]]/#[[2]]&/@Thread[{sp,Range[Length[sp]]}],IntegerQ]] (* The program generates the first 13 terms of the sequence. *) (* Harvey P. Dale, Aug 07 2025 *)

a(n) = A357741(n) / A106125(n).

cp's OEIS Frontend

A106125 Numbers k such that k divides the k-th semiprime.

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