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.

A046063 Numbers k such that the k-th partition number A000041(k) is prime.

Original entry on oeis.org

2, 3, 4, 5, 6, 13, 36, 77, 132, 157, 168, 186, 188, 212, 216, 302, 366, 417, 440, 491, 498, 525, 546, 658, 735, 753, 825, 841, 863, 1085, 1086, 1296, 1477, 1578, 1586, 1621, 1793, 2051, 2136, 2493, 2502, 2508, 2568, 2633, 2727, 2732, 2871, 2912, 3027, 3098, 3168, 3342, 3542, 3641, 4118
Offset: 1

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Author

Keywords

Comments

The corresponding primes are given in A049575. - Joerg Arndt, May 09 2013

Crossrefs

Programs

  • Mathematica
    Select[ Range@3341, PrimeQ@ PartitionsP@# &] (* Robert G. Wilson v *)
  • PARI
    for(n=0,10^5,my(p=numbpart(n));if(isprime(p),print1(n,", "))); \\ Joerg Arndt, May 09 2013
    
  • Python
    from sympy import isprime, npartitions
    print([n for n in range(1, 5001) if isprime(npartitions(n))]) # Indranil Ghosh, Apr 10 2017

Extensions

b-file extended by Max Alekseyev, Jul 07 2009, Jun 14 2011, Jan 08 2012, May 19 2014

A049575 Prime partition numbers.

Original entry on oeis.org

2, 3, 5, 7, 11, 101, 17977, 10619863, 6620830889, 80630964769, 228204732751, 1171432692373, 1398341745571, 10963707205259, 15285151248481, 10657331232548839, 790738119649411319, 18987964267331664557, 74878248419470886233, 1394313503224447816939
Offset: 1

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Author

Keywords

Crossrefs

Intersection of A000040 and A000041.
Cf. A038753, A065728. - Reinhard Zumkeller, Nov 03 2009

Programs

  • Mathematica
    lst={};Do[a=PartitionsP[n];If[PrimeQ[a],AppendTo[lst,a]],{n,2*6!}];lst (* Vladimir Joseph Stephan Orlovsky, Jun 14 2009 *)
    Select[PartitionsP[Range[1000]],PrimeQ] (* Harvey P. Dale, Mar 11 2013 *)
  • PARI
    for(n=0,10^3,my(p=numbpart(n));if(isprime(p),print1(p,", "))); \\ Joerg Arndt, May 09 2013

Formula

a(n) = A000041(A046063(n)) = A000040(A051143(n)). - M. F. Hasler, Oct 19 2008
A010051(a(n))*A167392(a(n)) = 1. - Reinhard Zumkeller, Nov 03 2009

Extensions

More terms from James Sellers and Christian G. Bower, Oct 15 1999.

A050811 Partition numbers rounded to nearest integer given by the Hardy-Ramanujan approximate formula.

Original entry on oeis.org

2, 3, 4, 6, 9, 13, 18, 26, 35, 48, 65, 87, 115, 152, 199, 258, 333, 427, 545, 692, 875, 1102, 1381, 1725, 2145, 2659, 3285, 4046, 4967, 6080, 7423, 9037, 10974, 13293, 16065, 19370, 23304, 27977, 33519, 40080, 47833, 56981, 67757, 80431, 95316
Offset: 1

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Author

Patrick De Geest, Oct 15 1999

Keywords

Comments

The mounting error seems to be approximately A035949(n-3), n >= 4. - Alonso del Arte, Jul 28 2011
This conjecture is false, for correct approximation see the formula below. - Vaclav Kotesovec, Apr 03 2017

References

  • John H. Conway and Richard K. Guy, The Book of Numbers, Copernicus Press, NY, 1996, p. 95.

Crossrefs

Programs

  • Maple
    A050811:=n->round(exp(Pi*sqrt(2*n/3))/(4*n*sqrt(3))): seq(A050811(n), n=1..70); # Wesley Ivan Hurt, Sep 11 2015
  • Mathematica
    f[n_] := Round[ E^(Sqrt[2n/3] Pi)/(4Sqrt[3] n)]; Array[f, 45] (* Alonso del Arte, May 21 2011, corrected by Robert G. Wilson v, Sep 11 2015 *)
  • PARI
    a(n)=round(exp(Pi*sqrt(2*n/3))/(4*n*sqrt(3))) \\ Charles R Greathouse IV, May 01 2012
  • UBASIC
    input N:print round(#e^(pi(1)*sqrt(2*N/3))/(4*N*sqrt(3)))
    

Formula

a(n) = round(exp(Pi*sqrt(2*n/3))/(4*n*sqrt(3))). - Alonso del Arte, May 21 2011
a(n) - A000041(n) ~ (1/Pi + Pi/72) * exp(sqrt(2*n/3)*Pi) / (4*sqrt(2)*n^(3/2)) * (1 - (9 + Pi^2/48)*Pi/((72 + Pi^2)*sqrt(6*n))). - Vaclav Kotesovec, Apr 03 2017

Extensions

a(1) = 1 replaced by 2, a(2) = 2 replaced by 3. - Alonso del Arte, D. S. McNeil, Aug 07 2011

A091689 Smallest partition number with n-th prime as factor.

Original entry on oeis.org

2, 3, 5, 7, 11, 3718, 386155, 627, 8349, 2436, 75175, 34262962, 14883, 3010, 526823, 281589, 386155, 1064144451, 124754, 63261, 105558, 2552338241, 4565, 1958, 75175, 101, 12132164, 118114304, 37274405776748077, 1505499, 37338, 6185689, 2323520, 966467, 90175434980549623
Offset: 1

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Author

Reinhard Zumkeller, Jan 29 2004

Keywords

Comments

Erdős conjectured that every prime divides at least one value of the partition function, see Ahlgren and Ono link.

Examples

			For n = 10, A000040(10) = 29: a(10) = A000041(26) = 2436 = 29*7*3*2*2, as 29 does not divide smaller partition numbers.
		

Crossrefs

Formula

a(n) = A000041(A091690(n)).

Extensions

More terms from Amiram Eldar, May 16 2025
Showing 1-4 of 4 results.