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.

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A064944 a(n) = Sum_{i|n, j|n, j >= i} j.

Original entry on oeis.org

1, 5, 7, 17, 11, 38, 15, 49, 34, 60, 23, 132, 27, 82, 82, 129, 35, 191, 39, 207, 112, 126, 47, 384, 86, 148, 142, 283, 59, 469, 63, 321, 172, 192, 172, 666, 75, 214, 202, 597, 83, 640, 87, 435, 403, 258, 95, 1016, 162, 485, 262, 511, 107, 812, 264, 813, 292, 324
Offset: 1

Views

Author

Vladeta Jovovic, Oct 28 2001

Keywords

Examples

			a(6) = max(1,1)+max(1,2)+max(1,3)+max(1,6)+max(2,2)+max(2,3)+max(2,6)+max(3,3)+max(3,6)+max(6,6)=38, or a(6) = dot_product(1,2,3,4)*(1,2,3,6)=1*1+2*2+3*3+4*6=38.
		

Crossrefs

Programs

  • Haskell
    a064944 = sum . zipWith (*) [1..] . a027750_row'
    -- Reinhard Zumkeller, Jul 14 2015
    
  • Maple
    with(numtheory): seq(add(i*sort(convert(divisors(n),'list'))[i],i=1..tau(n)), n=1..200);
  • Mathematica
    A064944[n_] := #.Range[Length[#]] & [Divisors[n]];
    Array[A064944, 100] (* Paolo Xausa, Aug 07 2025 *)
  • PARI
    a(n) = my(d=divisors(n)); sum(i=1, length(d), i*d[i]); \\ Harry J. Smith, Sep 30 2009
    
  • Python
    from sympy import divisors
    def A064944(n): return sum(a*b for a, b in enumerate(divisors(n),1)) # Chai Wah Wu, Aug 07 2025

Formula

a(n) = Sum_{i=1..tau(n)} i*d_i, where {d_i}, i=1..tau(n) is the increasing sequence of divisors of n.
a(n) = Sum_{i=1..A000005(n)} i*A027750(n, i). - Michel Marcus, Jun 10 2015
From Ridouane Oudra, Aug 01 2025: (Start)
a(n) = Sum_{d|n} (n/d)*A135539(n,d).
a(n) = A064946(n) + A000203(n).
a(n) = (A064948(n) + A000203(n))/2.
a(n) = A337360(n) - A064945(n).
a(n) = A064948(n) - A064946(n).
a(n) = A064840(n) - A064947(n). (End)

A263825 Total number c_{pi_1(B_1)}(n) of n-coverings over the first amphicosm.

Original entry on oeis.org

1, 7, 5, 23, 7, 39, 9, 65, 18, 61, 13, 143, 15, 87, 35, 183, 19, 182, 21, 245, 45, 151, 25, 465, 38, 189, 58, 375, 31, 429, 33, 549, 65, 277, 63, 806, 39, 327, 75, 875, 43, 663, 45, 719, 126, 439, 49, 1535, 66, 650, 95, 933, 55, 982, 91, 1425, 105, 637, 61, 2093
Offset: 1

Views

Author

N. J. A. Sloane, Oct 28 2015

Keywords

Crossrefs

Programs

  • Maple
    A263825 := proc(n)
        local a,l,m,s1,s2,s3,s4 ;
        # Theorem 2
        a := 0 ;
        for l in numtheory[divisors](n) do
            m := n/l ;
            s1 := 0 ;
            for twok in numtheory[divisors](m) do
                if type(twok,'even') then
                    k := twok/2 ;
                    s1 := s1+numtheory[sigma](k)*k ;
                end if;
            end do:
            s2 := 0 ;
            for d in numtheory[divisors](l) do
                s2 := s2+numtheory[mobius](l/d)*d^2*igcd(2,d) ;
            end do:
            s3 := 0 ;
            for k in numtheory[divisors](m) do
                s3 := s3+numtheory[sigma](m/k)*k ;
                if modp(m,2*k) = 0 then
                    s3 := s3-numtheory[sigma](m/2/k)*k ;
                end if;
            end do:
            s4 := 0 ;
            for twok in numtheory[divisors](m) do
                if type(twok,'even') then
                    s4 := s4+numtheory[sigma](m/twok)*twok ;
                    if modp(m,2*twok) = 0 then
                        s4 := s4-numtheory[sigma](m/2/twok)*twok ;
                    end if;
                end if;
            end do:
            a := a+A059376(l)*s1 + s2*s3 + A007434(l)*s4 ;
        end do:
        a/n ;
    end proc: # R. J. Mathar, Nov 03 2015
  • Mathematica
    A007434[n_] := Sum[ MoebiusMu[n/d] * d^2, {d, Divisors[n]}];
    A059376[n_] := Sum[ MoebiusMu[n/d] * d^3, {d, Divisors[n]}];
    A263825[n_] := Module[{a, l, m, s1, s2, s3, s4},
    a = 0;
    Do[m = n/l;
    s1 = 0; Do[If[EvenQ[twok], k = twok/2; s1 = s1 + DivisorSigma[1, k]*k], {twok, Divisors[m]}];
    s2 = 0; Do[s2 = s2 + MoebiusMu[l/d]*d^2*GCD[2, d], {d, Divisors[l]}];
    s3 = 0; Do[s3 = s3 + DivisorSigma[1, m/k]*k ; If[Mod[m, 2*k] == 0, s3 = s3 - DivisorSigma[1, m/2/k]*k], {k, Divisors[m]}];
    s4 = 0; Do[If[EvenQ[twok], s4 = s4 + DivisorSigma[1, m/twok]*twok; If[ Mod[m, 2*twok] == 0, s4 = s4 - DivisorSigma[1, m/2/twok]*twok]], {twok, Divisors[m]}]; a = a + A059376[l]*s1 + s2*s3 + A007434[l]*s4,
    {l, Divisors[n]}]; a/n
    ];
    Array[A263825, 60] (* Jean-François Alcover, Nov 21 2017, after R. J. Mathar *)
  • PARI
    A001001(n) = sumdiv(n, d, sigma(d) * d);
    A007434(n) = sumdiv(n, d, moebius(n\d) * d^2);
    A059376(n) = sumdiv(n, d, moebius(n\d) * d^3);
    A060640(n) = sumdiv(n, d, sigma(n\d) * d);
    EpiPcZn(n) = sumdiv(n, d, moebius(n\d) * d^2 * gcd(d,2));
    S1(n)      = if (n%2, 0, A001001(n\2));
    S11(n)     = A060640(n) - if(n%2, 0, A060640(n\2));
    S21(n)     = if (n%2, 0, 2*A060640(n\2)) - if (n%4, 0, 2*A060640(n\4));
    a(n) = { 1/n * sumdiv(n, d,
      A059376(d) * S1(n\d) + EpiPcZn(d) * S11(n\d) + A007434(d) * S21(n\d));
    };
    vector(60, n, a(n))  \\ Gheorghe Coserea, May 04 2016

A349143 a(n) = Sum_{d|n} A038040(d) * A348507(n/d), where A038040(n) = n*tau(n), A348507(n) = A003959(n) - n, and A003959 is fully multiplicative with a(p) = (p+1).

Original entry on oeis.org

0, 1, 1, 9, 1, 16, 1, 51, 13, 22, 1, 114, 1, 28, 25, 233, 1, 145, 1, 168, 31, 40, 1, 590, 21, 46, 106, 222, 1, 310, 1, 939, 43, 58, 37, 915, 1, 64, 49, 896, 1, 406, 1, 330, 262, 76, 1, 2570, 29, 297, 61, 384, 1, 1012, 49, 1202, 67, 94, 1, 2040, 1, 100, 340, 3489, 55, 598, 1, 492, 79, 574, 1, 4457, 1, 118, 360, 546, 55
Offset: 1

Views

Author

Antti Karttunen, Nov 08 2021

Keywords

Comments

Dirichlet convolution of A348507 with A038040, which is the Dirichlet convolution of the identity function (A000027) with itself.
Dirichlet convolution of the identity function (A000027) with A349140.
Dirichlet convolution of sigma (A000203) with A349141.
Dirichlet convolution of A060640 with A348971.

Crossrefs

Programs

  • Mathematica
    f[p_, e_] := (p + 1)^e; s[1] = 1; s[n_] := Times @@ f @@@ FactorInteger[n]; a[n_] := DivisorSum[n, #*DivisorSigma[0, #]*(s[n/#] - n/#) &]; Array[a, 100] (* Amiram Eldar, Nov 08 2021 *)
  • PARI
    A038040(n) = (n*numdiv(n));
    A003959(n) = { my(f = factor(n)); for(i=1, #f~, f[i, 1]++); factorback(f); };
    A348507(n) = (A003959(n) - n);
    A349143(n) = sumdiv(n,d,A038040(d)*A348507(n/d));

Formula

a(n) = Sum_{d|n} A038040(n/d) * A348507(d).
a(n) = Sum_{d|n} d * A349140(n/d).
a(n) = Sum_{d|n} A000203(d) * A349141(n/d).
a(n) = Sum_{d|n} A060640(d) * A348971(n/d).
For all n >= 1, a(n) >= A349123(n) >= A348983(n).

A068986 Numbers k such that Sum_{d|k} sigma(d)/d is an integer.

Original entry on oeis.org

1, 21, 105, 1050, 1155, 24921, 26565, 45150, 49842, 59455, 249210, 274131, 548262, 1129645, 1151325, 1248555, 1309350, 2302650, 2741310, 3388935, 4605300, 6305013, 12610026, 13417131, 14685385, 23722545, 25750550, 26834262, 30154410, 33388425, 42997750, 44056155
Offset: 1

Views

Author

Benoit Cloitre, Apr 06 2002

Keywords

Comments

Also numbers k that divide A060640(k). - Seiichi Manyama, May 08 2021

Crossrefs

Programs

  • Mathematica
    f[p_, e_] := ((e + 1)*p^(e + 2) - (e + 2)*p^(e + 1) + 1)/(p - 1)^2; q[1] = True; q[n_] := Divisible[Times @@ f @@@ FactorInteger[n], n]; Select[Range[10^6], q] (* Amiram Eldar, Dec 29 2024 *)
  • PARI
    for(n=1,10^7,if(frac(sumdiv(n,d, sigma(d)/d))==0,print1(n,",")))
    
  • PARI
    is(k) = {my(f = factor(k)); !(prod(i = 1, #f~, p = f[i, 1]; e = f[i, 2];  ((e + 1)*p^(e + 2) - (e + 2)*p^(e + 1) + 1)/(p - 1)^2) % k);} \\ Amiram Eldar, Dec 29 2024

Extensions

More terms from Jason Earls, Apr 09 2002
a(22)-a(25) from Jinyuan Wang, Apr 06 2020
a(26)-a(32) from Michel Marcus, Apr 06 2020

A061258 a(n) = Sum_{d|n} d*psi(d), where psi(d) is reduced totient function, cf. A002322.

Original entry on oeis.org

1, 3, 7, 11, 21, 21, 43, 27, 61, 63, 111, 53, 157, 129, 87, 91, 273, 183, 343, 151, 175, 333, 507, 117, 521, 471, 547, 305, 813, 261, 931, 347, 447, 819, 483, 431, 1333, 1029, 631, 327, 1641, 525, 1807, 781, 681, 1521, 2163, 373, 2101, 1563, 1095, 1103, 2757
Offset: 1

Views

Author

Vladeta Jovovic, Apr 21 2001

Keywords

Crossrefs

Programs

  • Haskell
    a061258 n = sum $ zipWith (*) ds $ map a002322 ds
                where ds = a027750_row n
    -- Reinhard Zumkeller, Sep 02 2014
    
  • Mathematica
    a[n_] := DivisorSum[n, # * CarmichaelLambda[#] &]; Array[a, 100] (* Amiram Eldar, Apr 13 2024 *)
  • PARI
    a(n) = sumdiv(n, d, d * lcm(znstar(d)[2])); \\ Amiram Eldar, Apr 13 2024

Formula

a(n) = Sum_{k = 1..A000005(n)} (A027750(n,k)*A002322(A027750(n,k))). - Reinhard Zumkeller, Sep 02 2014

A245211 a(n) = Sum_{(d

Original entry on oeis.org

0, 1, 1, 5, 1, 11, 1, 17, 7, 15, 1, 47, 1, 19, 17, 49, 1, 62, 1, 67, 21, 27, 1, 151, 11, 31, 34, 87, 1, 145, 1, 129, 29, 39, 25, 254, 1, 43, 33, 219, 1, 189, 1, 127, 104, 51, 1, 423, 15, 130, 41, 147, 1, 278, 33, 287, 45, 63, 1, 589, 1, 67, 132, 321, 37, 277
Offset: 1

Views

Author

Jaroslav Krizek, Jul 23 2014

Keywords

Comments

If q are proper divisors of n then values of sequence a(n) are the bending moments at point 0 of static forces of sizes tau(q) operating in places q on the cantilever as the nonnegative number axis of length n with support at point 0 by the schema: a(n) = Sum_{q | n} (q * tau(q)).
Number n = 144 is the smallest number n such that a(n) > n * tau(n) (see A245212 and A245214).
Conjecture: 21 is only number such that a(n) = n.

Examples

			For n = 21 with proper divisors [1, 3, 7] we have: a(21) = 7 * tau(7) + 3 * tau(3) + 1 * tau(1) = 7*2 + 3*2 + 1*1 = 21.
		

Crossrefs

Programs

  • Magma
    [(&+[d*#([e: e in Divisors(d)]): d in Divisors(n)])-(n*(#[d: d in Divisors(n)])): n in [1..1000]];
    
  • PARI
    a(n) = sumdiv(n, d, (dJens Kruse Andersen, Aug 13 2014

Formula

a(n) = A060640(n) - A038040(n) = Sum_{d | n} (d * tau(d)) - n*tau(n).
a(n) = A038040(n) - A245212(n).
a(n) = 1 for n = primes.
a(n) = n + 5 for even semiprimes q = 2p > 4 (see A100484) where p = odd prime.

A318491 a(n) is the numerator of Sum_{d|n} Sum_{j|d} 1/j.

Original entry on oeis.org

1, 5, 7, 17, 11, 35, 15, 49, 34, 11, 23, 119, 27, 75, 77, 129, 35, 85, 39, 187, 5, 115, 47, 343, 86, 135, 142, 255, 59, 77, 63, 321, 161, 175, 33, 289, 75, 195, 63, 539, 83, 25, 87, 391, 374, 235, 95, 301, 162, 43, 245, 459, 107, 355, 23, 105, 91, 295, 119, 1309, 123, 315, 170, 769, 297
Offset: 1

Views

Author

Ilya Gutkovskiy, Aug 27 2018

Keywords

Examples

			1, 5/2, 7/3, 17/4, 11/5, 35/6, 15/7, 49/8, 34/9, 11/2, 23/11, 119/12, 27/13, 75/14, 77/15, 129/16, ...
		

Crossrefs

Programs

  • Maple
    f:= proc(n) local d;
       numer(add(numtheory:-sigma(d)/d, d = numtheory:-divisors(n))) end proc:
    map(f, [$1..65]); # Robert Israel, Jan 13 2025
  • Mathematica
    Numerator[Table[Sum[DivisorSigma[-1, d], {d, Divisors[n]}], {n, 65}]]
    Numerator[Table[Sum[DivisorSigma[1, d]/d, {d, Divisors[n]}], {n, 65}]]
    Numerator[Table[Sum[d DivisorSigma[0, d], {d, Divisors[n]}]/n, {n, 65}]]
    nmax = 65; Rest[Numerator[CoefficientList[Series[Sum[DivisorSigma[1, k] x^k/(k (1 - x^k)), {k, 1, nmax}], {x, 0, nmax}], x]]]
    nmax = 65; Rest[Numerator[CoefficientList[Series[-Log[Product[(1 - x^k)^DivisorSigma[0, k], {k, 1, nmax}]], {x, 0, nmax}], x]]]
  • PARI
    a(n) = numerator(sumdiv(n, d, sumdiv(d, j, 1/j))); \\ Michel Marcus, Aug 28 2018

Formula

Numerators of coefficients in expansion of Sum_{k>=1} sigma(k)*x^k/(k*(1 - x^k)), where sigma(k) = sum of divisors of k (A000203).
Numerators of coefficients in expansion of -log(Product_{k>=1} (1 - x^k)^tau(k)), where tau(k) = number of divisors of k (A000005).
a(n) = numerator of Sum_{d|n} sigma(d)/d.
a(n) = numerator of (1/n)*Sum_{d|n} d*tau(d).
If p is a prime, a(p) = 2*p + 1.
Sum_{k=1..n} a(k)/A318492(k) ~ zeta(2) * n * (log(n) + 2*gamma - 1 + zeta'(2)/zeta(2)), where gamma is Euler's constant (A001620). - Amiram Eldar, Dec 25 2024

A127099 Triangle T(n,m) = A126988 *A127093 read by rows.

Original entry on oeis.org

1, 3, 2, 4, 0, 3, 7, 6, 0, 4, 6, 0, 0, 0, 5, 12, 8, 9, 0, 0, 6, 8, 0, 0, 0, 0, 0, 7, 15, 14, 0, 12, 0, 0, 0, 8, 13, 0, 12, 0, 0, 0, 0, 0, 9, 18, 12, 0, 0, 15, 0, 0, 0, 0, 10, 12, 0, 0, 0, 0, 0, 0, 0, 0, 0, 11, 28, 24, 21, 16, 0, 18, 0, 0, 0, 0, 0, 12, 14, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 13, 24, 16, 0, 0
Offset: 1

Views

Author

Gary W. Adamson, Jan 05 2007

Keywords

Comments

Multiply the infinite lower triangular matrices A126988 and A127093.

Examples

			First few rows of the triangle are:
1;
3, 2;
4, 0, 3;
7, 6, 0, 4;
6, 0, 0, 0, 5;
12, 8, 9, 0, 0, 6;
8, 0, 0, 0, 0, 0, 7;
15, 14, 0, 12, 0, 0, 0, 8;
13, 0, 12, 0, 0, 0, 0, 0, 9;
18, 12, 0, 0, 15, 0, 0, 0, 0, 10;
...
		

Crossrefs

Formula

T(n,m) = sum_{j=m..n} A126988(n,j)*A127093(j,m).
T(n,1) = A000203(n).

Extensions

Extended by R. J. Mathar, Aug 18 2009

A245212 a(n) = n * tau(n) - Sum_{(d

Original entry on oeis.org

1, 3, 5, 7, 9, 13, 13, 15, 20, 25, 21, 25, 25, 37, 43, 31, 33, 46, 37, 53, 63, 61, 45, 41, 64, 73, 74, 81, 57, 95, 61, 63, 103, 97, 115, 70, 73, 109, 123, 101, 81, 147, 85, 137, 166, 133, 93, 57, 132, 170, 163, 165, 105, 154, 187, 161, 183, 169, 117, 131, 121
Offset: 1

Views

Author

Jaroslav Krizek, Jul 23 2014

Keywords

Comments

If d are divisors of n then values of sequence a(n) are the bending moments at point 0 of static forces of sizes tau(d) operating in places d on the cantilever as the nonnegative number axis of length n with support at point 0 by the schema: a(n) = (n * tau(n)) - Sum_{(d
If a(n) = 0 then n must be > 10^7.
Conjecture: a(n) = sigma(n) iff n is a power of 2 (A000079).
Number n = 72 is the smallest number n such that a(n) < n (see A245213).
Number n = 144 is the smallest number n such that a(n) < 0 (see A245214).

Examples

			For n = 6 with divisors [1, 2, 3, 6] we have: a(6) = 6 * tau(6) - (3 * tau(3) + 2 * tau(2) + 1 * tau(1)) = 6*4 - (3*2+2*2+1*1) = 13.
		

Crossrefs

Programs

  • Magma
    [(2*(n*(#[d: d in Divisors(n)]))-(&+[d*#([e: e in Divisors(d)]): d in Divisors(n)])): n in [1..1000]];
    
  • PARI
    a(n) = sumdiv(n, d, (-1)^(dJens Kruse Andersen, Aug 13 2014

Formula

a(n) = A038040(n) - A245211(n).
a(n) = 2 * A038040(n) - A060640(n) = 2 * (n * tau(n)) - Sum_{d | n} (d * tau(d)).

A318492 a(n) is the denominator of Sum_{d|n} Sum_{j|d} 1/j.

Original entry on oeis.org

1, 2, 3, 4, 5, 6, 7, 8, 9, 2, 11, 12, 13, 14, 15, 16, 17, 9, 19, 20, 1, 22, 23, 24, 25, 26, 27, 28, 29, 6, 31, 32, 33, 34, 7, 18, 37, 38, 13, 40, 41, 2, 43, 44, 45, 46, 47, 16, 49, 5, 51, 52, 53, 27, 5, 8, 19, 58, 59, 60, 61, 62, 21, 64, 65, 66, 67, 4, 69, 14, 71, 36, 73, 74, 75
Offset: 1

Author

Ilya Gutkovskiy, Aug 27 2018

Keywords

Examples

			1, 5/2, 7/3, 17/4, 11/5, 35/6, 15/7, 49/8, 34/9, 11/2, 23/11, 119/12, 27/13, 75/14, 77/15, 129/16, ...
		

Crossrefs

Cf. A000005, A000203, A006171, A007429, A017665, A017666, A060640, A068986 (positions of 1's), A318491 (numerators).

Programs

  • Mathematica
    Denominator[Table[Sum[DivisorSigma[-1, d], {d, Divisors[n]}], {n, 75}]]
    Denominator[Table[Sum[DivisorSigma[1, d]/d, {d, Divisors[n]}], {n, 75}]]
    Denominator[Table[Sum[d DivisorSigma[0, d], {d, Divisors[n]}]/n, {n, 75}]]
    nmax = 75; Rest[Denominator[CoefficientList[Series[Sum[DivisorSigma[1, k] x^k/(k (1 - x^k)), {k, 1, nmax}], {x, 0, nmax}], x]]]
    nmax = 75; Rest[Denominator[CoefficientList[Series[-Log[Product[(1 - x^k)^DivisorSigma[0, k], {k, 1, nmax}]], {x, 0, nmax}], x]]]
  • PARI
    a(n) = denominator(sumdiv(n, d, sumdiv(d, j, 1/j))); \\ Michel Marcus, Aug 28 2018

Formula

Denominators of coefficients in expansion of Sum_{k>=1} sigma(k)*x^k/(k*(1 - x^k)), where sigma(k) = sum of divisors of k (A000203).
Denominators of coefficients in expansion of -log(Product_{k>=1} (1 - x^k)^tau(k)), where tau(k) = number of divisors of k (A000005).
a(n) = denominator of Sum_{d|n} sigma(d)/d.
a(n) = denominator of (1/n)*Sum_{d|n} d*tau(d).
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