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.

Previous Showing 11-20 of 198 results. Next

A023360 Number of compositions of n into prime parts.

Original entry on oeis.org

1, 0, 1, 1, 1, 3, 2, 6, 6, 10, 16, 20, 35, 46, 72, 105, 152, 232, 332, 501, 732, 1081, 1604, 2352, 3493, 5136, 7595, 11212, 16534, 24442, 36039, 53243, 78573, 115989, 171264, 252754, 373214, 550863, 813251, 1200554, 1772207, 2616338, 3862121, 5701553
Offset: 0

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Author

Keywords

Examples

			2; 3; 4 = 2+2; 5 = 2+3 = 3+2; 6 = 2+2+2 = 3+3; 7 = 2+2+3 = 2+3+2 = 3+2+2 = 2+5 = 5+2; etc.
		

References

  • S. R. Finch, Mathematical Constants, Cambridge, 2003, pp. 292-295.
  • Silvia Heubach and Toufik Mansour, Combinatorics of Compositions and Words, CRC Press, 2010.

Crossrefs

Cf. A000607 for the unordered (partition) version.

Programs

  • Maple
    a:= proc(n) option remember; `if`(n=0, 1, add(
         `if`(isprime(j), a(n-j), 0), j=1..n))
        end:
    seq(a(n), n=0..50);  # Alois P. Heinz, Feb 12 2021
  • Mathematica
    CoefficientList[ Series[1 / (1 - Sum[ x^Prime[i], {i, 15}]), {x, 0, 45}], x]
  • PARI
    {my(n=60); Vec(1/(1-sum(k=1, n, if(isprime(k), x^k, 0))) + O(x*x^n))} \\ Andrew Howroyd, Dec 28 2017

Formula

a(n) = Sum_{prime p<=n} a(n-p) with a(0)=1. - Henry Bottomley, Dec 15 2000
G.f.: 1/(1 - Sum_{k>=1} x^A000040(k)). - Andrew Howroyd, Dec 28 2017

A101048 Number of partitions of n into semiprimes (a(0) = 1 by convention).

Original entry on oeis.org

1, 0, 0, 0, 1, 0, 1, 0, 1, 1, 2, 0, 2, 1, 3, 2, 3, 1, 5, 3, 5, 4, 7, 4, 9, 7, 10, 8, 13, 10, 17, 13, 18, 17, 25, 21, 29, 25, 34, 34, 43, 37, 51, 49, 61, 59, 73, 69, 89, 87, 103, 103, 124, 122, 148, 149, 172, 176, 206, 208, 244, 248, 281, 293, 337, 344, 391, 405, 456, 479, 537, 553
Offset: 0

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Author

Reinhard Zumkeller, Nov 28 2004

Keywords

Comments

Semiprime analog of A000607. a(n) <= A002095(n). - Jonathan Vos Post, Oct 01 2007
Das, Robles, Zaharescu, & Zeindler give an asymptotic formula, see Links. - Charles R Greathouse IV, Jan 20 2023

Examples

			a(12) = #{6 + 6, 4 + 4 + 4} = #{2 * (2*3), 3 * (2*2)} = 2.
		

Crossrefs

Programs

  • Haskell
    a101048 = p a001358_list where
       p _          0 = 1
       p ks'@(k:ks) m = if m < k then 0 else p ks' (m - k) + p ks m
    -- Reinhard Zumkeller, Mar 21 2014
    
  • Maple
    g:=1/product(product(1-x^(ithprime(i)*ithprime(j)),i=1..j),j=1..30): gser:=series(g,x=0,75): seq(coeff(gser,x,n),n=1..71); # Emeric Deutsch, Apr 04 2006
    # second Maple program:
    h:= proc(n) option remember; `if`(n=0, 0,
         `if`(numtheory[bigomega](n)=2, n, h(n-1)))
        end:
    b:= proc(n, i) option remember; `if`(n=0, 1, `if`(i<1, 0,
         `if`(i>n, 0, b(n-i, h(min(n-i, i))))+b(n, h(i-1))))
        end:
    a:= n-> b(n, h(n)):
    seq(a(n), n=0..100);  # Alois P. Heinz, May 19 2021
  • Mathematica
    terms = 100; CoefficientList[1/Product[1 - x^(Prime[i] Prime[j]), {i, 1, PrimePi[Ceiling[terms/2]]}, {j, 1, i}] + O[x]^terms, x] (* Jean-François Alcover, Aug 01 2018 *)
  • PARI
    issemi(n)=if(n<4, return(0)); forprime(p=2,97, if(n%p==0, return(isprime(n/p)))); bigomega(n)==2
    allsemi(v)=for(i=1,#v, if(!issemi(v[i]), return(0))); 1
    a(n)=my(s); if(n<4, return(n==0)); forpart(k=n, if(allsemi(k), s++),[4,n]); s \\ Charles R Greathouse IV, Jan 20 2023

Formula

G.f.: 1/product(product(1-x^(p(i)p(j)), i = 1..j),j = 1..infinity), p(k) is the k-th prime. - Emeric Deutsch, Apr 04 2006

Extensions

a(0) set to 1 by N. J. A. Sloane, Nov 23 2007

A316523 Number of odd multiplicities minus number of even multiplicities in the canonical prime factorization of n.

Original entry on oeis.org

0, 1, 1, -1, 1, 2, 1, 1, -1, 2, 1, 0, 1, 2, 2, -1, 1, 0, 1, 0, 2, 2, 1, 2, -1, 2, 1, 0, 1, 3, 1, 1, 2, 2, 2, -2, 1, 2, 2, 2, 1, 3, 1, 0, 0, 2, 1, 0, -1, 0, 2, 0, 1, 2, 2, 2, 2, 2, 1, 1, 1, 2, 0, -1, 2, 3, 1, 0, 2, 3, 1, 0, 1, 2, 0, 0, 2, 3, 1, 0, -1, 2, 1, 1
Offset: 1

Views

Author

Gus Wiseman, Jul 05 2018

Keywords

Crossrefs

Cf. A187039 (where a(n)=0). - Michel Marcus, Jul 08 2018

Programs

  • Maple
    f:= proc(n) local F;
      F:= map(t -> t[2],ifactors(n)[2]);
      2*nops(select(type,F,odd))-nops(F);
    end proc:
    map(f, [$1..100]); # Robert Israel, Aug 27 2018
  • Mathematica
    Table[Total[-(-1)^If[n==1,{},FactorInteger[n][[All,2]]]],{n,100}]
  • PARI
    a(n) = my(f=factor(n)); -sum(k=1, #f~, (-1)^(f[k,2])); \\ Michel Marcus, Jul 08 2018; corrected Jun 13 2022

Formula

If i and j are coprime, a(i*j) = a(i)+a(j). - Robert Israel, Aug 27 2018
From Amiram Eldar, Oct 05 2023: (Start)
Additive with a(p^e) = (-1)^(e+1).
a(n) = A162642(n) - A162641(n).
Sum_{k=1..n} a(k) = n * log(log(n)) + c * n + O(n/log(n)), where c = A077761 - 2*A179119 = -0.398962... . (End)

A106244 Number of partitions into distinct prime powers.

Original entry on oeis.org

1, 1, 1, 2, 2, 3, 3, 4, 5, 6, 7, 8, 10, 11, 13, 14, 17, 19, 21, 24, 27, 30, 33, 37, 41, 46, 50, 56, 62, 68, 75, 82, 91, 99, 108, 118, 129, 141, 152, 166, 180, 196, 211, 229, 248, 267, 288, 310, 335, 360, 387, 415, 447, 479, 513, 549, 589, 630, 672, 719, 768, 820, 873, 930
Offset: 0

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Author

Reinhard Zumkeller, Apr 26 2005

Keywords

Comments

A054685(n) < a(n) < A023893(n) for n>2.

Examples

			a(10) = #{3^2+1,2^3+2,7+3,7+2+1,5+2^2+1,5+3+2,2^2+3+2+1} = 7.
		

Crossrefs

Programs

  • Haskell
    import Data.MemoCombinators (memo2, integral)
    a106244 n = a106244_list !! n
    a106244_list = map (p' 1) [0..] where
       p' = memo2 integral integral p
       p _ 0 = 1
       p k m = if m < pp then 0 else p' (k + 1) (m - pp) + p' (k + 1) m
               where pp = a000961 k
    -- Reinhard Zumkeller, Nov 24 2015
  • Maple
    g:=(1+x)*(product(product(1+x^(ithprime(k)^j),j=1..5),k=1..20)): gser:=series(g,x=0,68): seq(coeff(gser,x,n),n=1..63); # Emeric Deutsch, Aug 27 2007
  • Mathematica
    m = 64; gf = (1+x)*Product[1+x^(Prime[k]^j), {j, 1, 5}, {k, 1, 18}] + O[x]^m; CoefficientList[gf, x] (* Jean-François Alcover, Mar 02 2019, from Maple *)
  • PARI
    lista(m) = {x = t + t*O(t^m); gf = (1+x)*prod(k=1, m, if (isprimepower(k),(1+x^k), 1)); for (n=0, m, print1(polcoeff(gf, n, t), ", "));} \\ Michel Marcus, Mar 02 2019
    

Formula

a(n) = A054685(n-1)+A054685(n). - Vladeta Jovovic, Apr 28 2005
G.f.: (1+x)*Product(Product(1+x^(p(k)^j), j=1..infinity),k=1..infinity), where p(k) is the k-th prime (offset 0). - Emeric Deutsch, Aug 27 2007

Extensions

Offset corrected and a(0)=1 added by Reinhard Zumkeller, Nov 24 2015

A056768 Number of partitions of the n-th prime into parts that are all primes.

Original entry on oeis.org

1, 1, 2, 3, 6, 9, 17, 23, 40, 87, 111, 219, 336, 413, 614, 1083, 1850, 2198, 3630, 5007, 5861, 9282, 12488, 19232, 33439, 43709, 49871, 64671, 73506, 94625, 221265, 279516, 394170, 441250, 766262, 853692, 1175344, 1608014, 1975108, 2675925
Offset: 1

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Author

Brian Galebach, Aug 16 2000

Keywords

Examples

			a(4) = 3 because the 4th prime is 7 which can be partitioned using primes in 3 ways: 7, 5 + 2, and 3 + 2 + 2.
In connection with the 6th prime 13, for instance, we have the a(6) = 9 prime partitions: 13 = 2 + 2 + 2 + 2 + 2 + 3 = 2 + 2 + 2 + 2 + 5 = 2 + 2 + 2 + 7 = 2 + 2 + 3 + 3 + 3 = 2 + 3 + 3 + 5 = 2 + 11 = 3 + 3 + 7 = 3 + 5 + 5.
		

Crossrefs

Cf. A000041, A000607, A100118, A276687, A070215 (distinct parts).

Programs

Formula

a(n) = A000607(prime(n)).
a(n) = A168470(n) + 1. - Alonso del Arte, Feb 15 2014, restating the corresponding formula given by R. J. Mathar for A168470.
a(n) = [x^prime(n)] Product_{k>=1} 1/(1 - x^prime(k)). - Ilya Gutkovskiy, Jun 05 2017

Extensions

More terms from James Sellers, Aug 25 2000

A319169 Number of integer partitions of n whose parts all have the same number of prime factors, counted with multiplicity.

Original entry on oeis.org

1, 1, 2, 2, 3, 3, 4, 4, 6, 6, 8, 7, 11, 11, 14, 15, 20, 19, 26, 27, 34, 35, 43, 45, 59, 60, 72, 77, 94, 98, 118, 125, 148, 158, 184, 198, 233, 245, 282, 308, 353, 374, 428, 464, 525, 566, 635, 686, 779, 832, 930, 1005, 1123, 1208, 1345, 1451, 1609, 1732, 1912
Offset: 0

Views

Author

Gus Wiseman, Oct 10 2018

Keywords

Examples

			The a(1) = 1 through a(9) = 6 integer partitions:
  1  2   3    4     5      6       7        8         9
     11  111  22    32     33      52       44        72
              1111  11111  222     322      53        333
                           111111  1111111  332       522
                                            2222      3222
                                            11111111  111111111
		

Crossrefs

Programs

  • Maple
    b:= proc(n, i, f) option remember; `if`(n=0, 1, `if`(i<1, 0,
          b(n, i-1, f)+(o-> `if`(f in {0, o}, b(n-i, min(i, n-i),
         `if`(f=0, o, f)), 0))(numtheory[bigomega](i))))
        end:
    a:= n-> b(n$2, 0):
    seq(a(n), n=0..75);  # Alois P. Heinz, Dec 15 2018
  • Mathematica
    Table[Length[Select[IntegerPartitions[n],SameQ@@PrimeOmega/@#&]],{n,30}]
    (* Second program: *)
    b[n_, i_, f_] := b[n, i, f] = If[n == 0, 1, If[i < 1, 0,
         b[n, i-1, f] + Function[o, If[f == 0 || f == o, b[n-i, Min[i, n-i],
         If[f == 0, o, f]], 0]][PrimeOmega[i]]]];
    a[n_] := b[n, n, 0];
    a /@ Range[0, 75] (* Jean-François Alcover, May 10 2021, after Alois P. Heinz *)

Extensions

a(51)-a(58) from Chai Wah Wu, Nov 12 2018

A117278 Triangle read by rows: T(n,k) is the number of partitions of n into k prime parts (n>=2, 1<=k<=floor(n/2)).

Original entry on oeis.org

1, 1, 0, 1, 1, 1, 0, 1, 1, 1, 1, 1, 0, 1, 1, 1, 0, 1, 2, 1, 0, 2, 1, 1, 1, 1, 0, 2, 2, 1, 0, 1, 2, 2, 1, 1, 1, 1, 2, 2, 2, 1, 0, 2, 1, 3, 2, 1, 1, 0, 1, 3, 2, 3, 2, 1, 0, 2, 2, 3, 3, 2, 1, 1, 1, 0, 4, 3, 3, 3, 2, 1, 0, 2, 2, 4, 3, 4, 2, 1, 1, 1, 1, 3, 4, 5, 3, 3, 2, 1, 0, 2, 2, 6, 4, 4, 4, 2, 1, 1, 0, 1, 5, 3, 6
Offset: 2

Views

Author

Emeric Deutsch, Mar 07 2006

Keywords

Comments

Row n has floor(n/2) terms. Row sums yield A000607. T(n,1) = A010051(n) (the characteristic function of the primes). T(n,2) = A061358(n). Sum(k*T(n,k), k>=1) = A084993(n).

Examples

			T(12,3) = 2 because we have [7,3,2] and [5,5,2].
Triangle starts:
  1;
  1;
  0, 1;
  1, 1;
  0, 1, 1;
  1, 1, 1;
  0, 1, 1, 1;
  0, 1, 2, 1;
  ...
		

Crossrefs

Row sums give A000607.
T(A000040(n),n) gives A259254(n).

Programs

  • Maple
    g:=1/product(1-t*x^(ithprime(j)),j=1..30): gser:=simplify(series(g,x=0,30)): for n from 2 to 22 do P[n]:=sort(coeff(gser,x^n)) od: for n from 2 to 22 do seq(coeff(P[n],t^j),j=1..floor(n/2)) od; # yields sequence in triangular form
    # second Maple program:
    b:= proc(n, i) option remember;
          `if`(n=0, [1], `if`(i<1, [], zip((x, y)->x+y, b(n, i-1),
           [0, `if`(ithprime(i)>n, [], b(n-ithprime(i), i))[]], 0)))
        end:
    T:= n-> subsop(1=NULL, b(n, numtheory[pi](n)))[]:
    seq(T(n), n=2..25);  # Alois P. Heinz, Nov 16 2012
  • Mathematica
    (* As triangle: *) nn=20;a=Product[1/(1-y x^i),{i,Table[Prime[n],{n,1,nn}]}];Drop[CoefficientList[Series[a,{x,0,nn}],{x,y}],2,1]//Grid (* Geoffrey Critzer, Oct 30 2012 *)
  • PARI
    parts(n, pred)={prod(k=1, n, if(pred(k), 1/(1-y*x^k) + O(x*x^n), 1))}
    {my(n=15); apply(p->Vecrev(p/y), Vec(parts(n, isprime)-1))} \\ Andrew Howroyd, Dec 28 2017

Formula

G.f.: G(t,x) = -1+1/product(1-tx^(p(j)), j=1..infinity), where p(j) is the j-th prime.

A051034 Minimal number of primes needed to sum to n.

Original entry on oeis.org

1, 1, 2, 1, 2, 1, 2, 2, 2, 1, 2, 1, 2, 2, 2, 1, 2, 1, 2, 2, 2, 1, 2, 2, 2, 3, 2, 1, 2, 1, 2, 2, 2, 3, 2, 1, 2, 2, 2, 1, 2, 1, 2, 2, 2, 1, 2, 2, 2, 3, 2, 1, 2, 2, 2, 3, 2, 1, 2, 1, 2, 2, 2, 3, 2, 1, 2, 2, 2, 1, 2, 1, 2, 2, 2, 3, 2, 1, 2, 2, 2, 1, 2, 2, 2, 3, 2, 1, 2, 2, 2, 3, 2, 3, 2, 1, 2, 2, 2, 1, 2, 1, 2, 2, 2, 1, 2, 1, 2, 2, 2
Offset: 2

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Author

Keywords

Examples

			a(2) = 1 because 2 is already prime.
a(4) = 2 because 4 = 2+2 is a partition of 4 into 2 prime parts and there is no such partition with fewer terms.
a(27) = 3 because 27 = 3+5+19 is a partition of 27 into 3 prime parts and there is no such partition with fewer terms.
		

Crossrefs

Programs

  • Mathematica
    (* Assuming Goldbach's conjecture *) a[p_?PrimeQ] = 1; a[n_] := If[ Reduce[ n == x + y, {x, y}, Primes] === False, 3, 2]; Table[a[n], {n, 2, 112}] (* Jean-François Alcover, Apr 03 2012 *)
  • PARI
    issum(n,k)=if(k==1,isprime(n),k--;forprime(p=2,n,if(issum(n-p,k),return(1)));0)
    a(n)=my(k);while(!issum(n,k++),);k \\ Charles R Greathouse IV, Jun 01 2011

Formula

a(n) = 1 iff n is prime. a(2n) = 2 (for n > 1) if Goldbach's conjecture is true. a(2n+1) = 2 (for n >= 1) if 2n+1 is not prime, but 2n-1 is. a(2n+1) >= 3 (for n >= 1) if both 2n+1 and 2n-1 are not primes (for sufficiently large n, a(2n+1) = 3 by Vinogradov's theorem, 1937). - Franz Vrabec, Nov 30 2004
a(n) <= 3 for all n, assuming the Goldbach conjecture. - N. J. A. Sloane, Jan 20 2007
a(2n+1) <= 5, see Tao 2012. - Charles R Greathouse IV, Jul 09 2012
Assuming Goldbach's conjecture, a(n) <= 3. In particular, a(p)=1; a(2*n)=2 for n>1; a(p+2)=2 provided p+2 is not prime; otherwise a(n)=3. - Sean A. Irvine, Jul 29 2019
a(2n+1) <= 3 by Helfgott's proof of Goldbach's ternary conjecture, and hence a(n) <= 4 in general. - Charles R Greathouse IV, Oct 24 2022

Extensions

More terms from Naohiro Nomoto, Mar 16 2001

A280917 Expansion of 1/(1 - x - Sum_{k>=1} x^prime(k)).

Original entry on oeis.org

1, 1, 2, 4, 7, 14, 26, 50, 95, 180, 343, 652, 1240, 2359, 4486, 8532, 16227, 30862, 58697, 111636, 212321, 403814, 768015, 1460691, 2778094, 5283667, 10049027, 19112282, 36349721, 69133673, 131485594, 250072951, 475614693, 904573387, 1720411555, 3272057256, 6223138101, 11835809946, 22510571803, 42812941849
Offset: 0

Views

Author

Ilya Gutkovskiy, Jan 10 2017

Keywords

Comments

Number of compositions (ordered partitions) of n into prime parts (1 included) (A008578).

Examples

			a(4) = 7 because we have [3, 1], [2, 2], [2, 1, 1], [1, 3], [1, 2, 1], [1, 1, 2] and [1, 1, 1, 1].
		

Crossrefs

Programs

  • Mathematica
    nmax = 39; CoefficientList[Series[1/(1 - x - Sum[x^Prime[k], {k, 1, nmax}]), {x, 0, nmax}], x]
  • PARI
    Vec(1 / (1 - x - sum(k=1, 100,  x^prime(k))) + O(x^100)) \\ Indranil Ghosh, Mar 09 2017

Formula

G.f.: 1/(1 - x - Sum_{k>=1} x^prime(k)).

A331416 Irregular triangle read by rows where T(n,k) is the number of integer partitions y of n such that Sum_i prime(y_i) = k.

Original entry on oeis.org

1, 0, 0, 1, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0, 2, 1, 0, 0, 0, 0, 0, 0, 1, 3, 1, 0, 0, 0, 0, 0, 0, 0, 0, 2, 3, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 4, 3, 1, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 5, 3, 2, 2, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 4, 6, 3, 4, 2
Offset: 0

Views

Author

Gus Wiseman, Jan 17 2020

Keywords

Examples

			Triangle begins:
  1
  0 0 1
  0 0 0 1 1
  0 0 0 0 0 2 1
  0 0 0 0 0 0 1 3 1
  0 0 0 0 0 0 0 0 2 3 1 1
  0 0 0 0 0 0 0 0 0 1 4 3 1 2
  0 0 0 0 0 0 0 0 0 0 0 2 5 3 2 2 0 1
  0 0 0 0 0 0 0 0 0 0 0 0 1 4 6 3 4 2 0 2
  0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 6 6 4 6 2 1 2 0 1
  0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 4 8 6 6 7 2 4 2 0 1 0 0 0 1
  0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 6 9 7 9 7 3 7 2 1 1 0 0 0 2
Row n = 8 counts the following partitions (empty column not shown):
  (2222)  (332)    (44)      (41111)    (53)        (611)   (8)
          (422)    (431)     (311111)   (62)        (5111)  (71)
          (3221)   (3311)    (2111111)  (521)
          (22211)  (4211)               (11111111)
                   (32111)
                   (221111)
Column k = 19 counts the following partitions:
  (8)   (6111)   (532)        (443)       (33222)
  (71)  (51111)  (622)        (4331)      (42222)
                 (5221)       (4421)      (322221)
                 (4111111)    (33311)     (2222211)
                 (31111111)   (43211)
                 (211111111)  (332111)
                              (422111)
                              (3221111)
                              (22211111)
		

Crossrefs

Row lengths are A331417.
Row sums are A000041.
Column sums are A000607.
Shifting row n to the left n times gives A331385.
Partitions whose Heinz number is divisible by their sum of primes: A330953.
Partitions of whose sum of primes is divisible by their sum are A331379.
Partitions whose product divides their sum of primes are A331381.
Partitions whose product equals their sum of primes are A331383.

Programs

  • Mathematica
    maxm[n_]:=Max@@Table[Total[Prime/@y],{y,IntegerPartitions[n]}];
    Table[Length[Select[IntegerPartitions[n],Total[Prime/@#]==k&]],{n,0,10},{k,0,maxm[n]}]
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