cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

Showing 1-4 of 4 results.

A089543 Lesser prime factor of semiprimes in A089542.

Original entry on oeis.org

2, 2, 3, 7, 53, 29, 353, 1549, 8353, 7, 15889, 1691419, 347, 67, 1097, 274177, 43, 18882774223, 67, 5197, 1801088543, 556114086547, 44773, 3062989, 5641, 92553847628747, 18349361, 607, 51131, 13217, 42806180589950051
Offset: 1

Views

Author

Ray Chandler, Nov 09 2003

Keywords

Crossrefs

Cf. A085753, A089542, A089544.

A089544 Greater prime factor of semiprimes in A089542.

Original entry on oeis.org

2, 2, 11, 37, 59, 1609, 2333, 10831, 46381, 1428571429, 17956553, 5271373, 872838923897, 165850848142657, 399174011286107, 67280421310721, 19238145625263645679, 2083719670141, 29528651577019605807821
Offset: 1

Views

Author

Ray Chandler, Nov 09 2003

Keywords

Crossrefs

Cf. A085753, A089542, A089543.

A089539 a(n) is the least semiprime > n!.

Original entry on oeis.org

4, 4, 9, 25, 121, 721, 5041, 40321, 362885, 3628801, 39916803, 479001617, 6227020801, 87178291201, 1307674368007, 20922789888002, 355687428096003, 6402373705728023, 121645100408832001, 2432902008176640001, 51090942171709440011, 1124000727777607680029, 25852016738884976640003
Offset: 1

Views

Author

Ray Chandler, Nov 09 2003

Keywords

Crossrefs

Cf. A001358, A085747, A089538, A089540, A089541, A089542.

Programs

  • Mathematica
    lsn[n_]:=Module[{sp=n!+1},While[PrimeOmega[sp]!=2,sp++];sp]; Array[lsn,25] (* Harvey P. Dale, Mar 30 2024 *)

Formula

a(n) = n! + A085747(n).

Extensions

Better name, more terms from Jinyuan Wang, Jul 31 2021

A085753 Least k such that n^n + k is a semiprime.

Original entry on oeis.org

3, 0, 6, 3, 2, 5, 6, 3, 4, 3, 6, 31, 6, 3, 4, 1, 20, 19, 28, 3, 8, 3, 60, 5, 16, 15, 46, 3, 2, 7, 12, 13, 4, 3, 18, 3, 9, 3, 32, 7, 6, 37, 30, 61, 2, 81, 26, 5, 34, 79, 62, 6, 44, 5, 16, 15, 10, 133, 12, 31, 28, 49, 26, 21, 92, 43, 76, 67, 38, 57, 36, 43, 21, 115, 2, 25, 74, 179, 28, 27, 52, 15
Offset: 1

Views

Author

Jason Earls, Jul 21 2003

Keywords

Links

Crossrefs

Cf. A001358 (semiprimes), A089542, A089543, A089544.

Programs

  • Mathematica
    PrimeFactorExponentsAdded[n_] := Plus @@ Flatten[ Table[ # [[2]], {1}] & /@ FactorInteger[n]]; f[n_] := Block[{k = 0}, While[ PrimeFactorExponentsAdded[n^n + k] != 2, k++ ]; k]; Table[ f[n], {n, 1, 40}]
Table[Module[{k=0,c=n^n},While[PrimeOmega[c+k]!=2,k++];k],{n,82}] (* Harvey P. Dale, Aug 02 2025 *)
  • PARI
    a(n) = my(k=0); while (bigomega(n^n+k) != 2, k++); k; \\ Michel Marcus, Jul 21 2020

Extensions

Edited and extended by Robert G. Wilson v, Aug 14 2003
Corrected and extended by Ray Chandler, Nov 22 2003
a(69)-a(82) from Max Alekseyev, Jun 13 2009
a(52) and a(73) corrected by Sean A. Irvine, Jul 20 2020
Showing 1-4 of 4 results.

Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

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