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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A363177 Primitive abundant numbers (A071395) that are cubefull numbers (A036966).

Original entry on oeis.org

26376098024367, 33912126031329, 1910383099764867, 2792098376579421, 5229860083034911875, 6886512413632368153, 8815747507513708671, 28966027524687899919, 42200802302982406288, 89594138836162749375, 224439112362213402759, 288564573037131517833, 512767531125033485625
Offset: 1

Views

Author

Amiram Eldar, May 19 2023

Keywords

Comments

It seems that this sequence is also the intersection of A036966 and A091191 (checked up to 10^27).
Are there terms that are 4-full numbers (A036967)? There are none below 10^27.

Crossrefs

Intersection of A036966 and A071395.
Subsequence of A363169 and A363175.
A306797 is a subsequence.

A210470 Powerful numbers (A001694) which can be written as the sum of two relatively prime 3-powerful numbers (A036966) different from 1.

Original entry on oeis.org

841, 968, 2312, 3528, 5041, 5776, 12769, 14884, 16641, 45125, 51984, 109561, 123823, 157609, 168921, 207576, 373321, 450241, 498436, 609725, 711828, 731025, 798768, 940896, 1223048, 1590121, 1792921, 2478843, 2481992, 2526752, 3157729, 3964081, 5346675, 6255001
Offset: 1

Views

Author

N. J. A. Sloane, Apr 22 2013

Keywords

Examples

			841 = 216+625 ; 968 = 343+625 ; 2312=125+2187;
		

References

  • Jean-Marie de Konninck, Those Fascinating Numbers, Amer. Math. Soc., 2009.
  • Alonso Del Arte, Posting to the Sequence Fans Mailing List, Mar 10 2011.

Crossrefs

Programs

  • Maple
    isA210470 := proc(n)
        if isA001694(n) then
            for i from 2 do
                p3 := A036966(i) ;
                if p3+2 > n then
                    return false;
                end if;
                p3comp := n-p3 ;
                if isA036966(p3comp) and igcd(p3,p3comp) = 1 then
                    # print(n,p3,p3comp) ;
                    return true;
                end if;
            end do:
            return false;
        else
            return false;
        end if;
    end proc:
    for n from 1 do
        if isA210470(n) then
            printf("%d,",n) ;
        end if;
    end do: # R. J. Mathar, May 01 2013
  • Mathematica
    With[{max = 10^7}, powQ[n_, e_] := Min[FactorInteger[n][[;; , 2]]] > e; pows = Union[Flatten[Table[i^2*j^3, {j, max^(1/3)}, {i, Sqrt[max/j^3]}]]]; Select[Union[Plus @@@ Select[Tuples[Select[pows, powQ[#, 2] &], {2}], CoprimeQ @@ # &]], # < max && powQ[#, 1] &]] (* Amiram Eldar, Jan 30 2023 *)

Formula

{ a in A001694: a=b+c and b,c >1 and b,c in A036966 and gcd(b,c)=1}. - R. J. Mathar, May 01 2013

Extensions

More terms from Amiram Eldar, Jan 30 2023

A362972 Squarefree kernels of cubefull numbers (A036966).

Original entry on oeis.org

1, 2, 2, 3, 2, 2, 3, 5, 2, 6, 3, 2, 7, 6, 2, 5, 6, 3, 6, 10, 2, 6, 11, 6, 6, 10, 2, 3, 13, 7, 6, 14, 5, 15, 6, 6, 10, 2, 17, 10, 6, 14, 6, 3, 19, 6, 6, 10, 2, 21, 10, 15, 6, 22, 14, 6, 23, 6, 11, 6, 5, 10, 2, 7, 15, 6, 26, 14, 3, 10, 6, 22, 14, 6, 29, 10, 30, 6
Offset: 1

Views

Author

Amiram Eldar, May 13 2023

Keywords

Examples

			A036966(2) = 8 = 2^3, therefore a(2) = 2.
A036966(10) = 216 = 2^3 * 3^2, therefore a(10) = 2 * 3 = 6.
		

Crossrefs

Programs

  • Mathematica
    seq[kmax_] := Module[{s = {1}}, Do[f = FactorInteger[k]; If[Min@f[[;; , 2]] > 2, AppendTo[s, Times @@ f[[;; , 1]]]], {k, 2, kmax}]; s]; seq[10^5]
  • PARI
    lista(kmax) = {my(f); for(k = 1, kmax, f = factor(k); if(k==1 || vecmin(f[, 2]) > 2, print1(vecprod(f[, 1]), ", ")));}

Formula

a(n) = A007947(A036966(n)).
Sum_{A036966(k) < x} a(k) = c * x^(2/3) + o(x^(2/3)), where c = (3/Pi^2) * Product_{p prime} (1 + 1/((p+1)*(p^(2/3)-1))) = 0.7356919531... (Jakimczuk, 2017). [corrected Sep 21 2024]
Sum_{k=1..n} a(k) ~ (c / A362974 ^ 2) * n^2, where c is the constant above.

A363013 a(n) is the number of prime factors (counted with multiplicity) of the n-th cubefull number (A036966).

Original entry on oeis.org

0, 3, 4, 3, 5, 6, 4, 3, 7, 6, 5, 8, 3, 7, 9, 4, 7, 6, 8, 6, 10, 8, 3, 9, 8, 7, 11, 7, 3, 4, 9, 6, 5, 6, 10, 9, 8, 12, 3, 7, 10, 7, 9, 8, 3, 11, 10, 9, 13, 6, 8, 7, 11, 6, 8, 10, 3, 12, 4, 11, 6, 10, 14, 5, 7, 10, 6, 7, 9, 9, 12, 7, 9, 11, 3, 8, 9, 13, 7, 4, 3
Offset: 1

Views

Author

Amiram Eldar, May 13 2023

Keywords

Crossrefs

Similar sequences: A072047, A076399, A360729.

Programs

  • Mathematica
    PrimeOmega[Select[Range[10000], # == 1 || Min[FactorInteger[#][[;; , 2]]] > 2 &]]
  • PARI
    iscubefull(n) = n==1 || vecmin(factor(n)[, 2]) > 2;
    apply(bigomega, select(iscubefull, [1..10000]))

Formula

a(n) = A001222(A036966(n)).
a(n) >= 3, for n > 1.
Sum_{A036966(k) < x} a(k) = 3*c*x^(1/3)*log(log(x)) + (3*(B_2 - log(2)) + Sum_{p prime} ((4*p^(1/3)+5)/(p^(5/3)+p^(1/3)+1)))*c*x^(1/3) + O(x^(1/3)/sqrt(log(x))), where B_2 = A083342 and c = A362974 (Jakimczuk and Lalín, 2022). [corrected Sep 21 2024]

A363014 Cubefull numbers (A036966) with a record gap to the next cubefull number.

Original entry on oeis.org

1, 8, 16, 32, 81, 128, 343, 512, 729, 864, 1024, 1331, 3456, 4096, 6912, 8192, 12167, 25000, 32768, 35937, 43904, 46656, 55296, 70304, 93312, 110592, 117649, 140608, 186624, 287496, 331776, 357911, 373248, 592704, 707281, 889056, 1000000, 1124864, 1157625, 1296000
Offset: 1

Views

Author

Amiram Eldar, May 13 2023

Keywords

Comments

This sequence is infinite since the asymptotic density of the cubefull numbers is 0.
The corresponding record gaps are 7, 8, 16, 49, 47, 215, 169, 217, 135, 160, ... .

Examples

			The sequence of cubefull numbers begins with 1, 8, 16, 27, 32, 64, 81 and 125. The differences between these terms are 7, 8, 11, 5, 32, 17 and 44. The record values, 7, 8, 11, 32 and 44 occur after the cubefull numbers 1, 8, 16, 32 and 81, the first 5 terms of this sequence.
		

Crossrefs

Programs

  • Mathematica
    cubQ[n_] := Min[FactorInteger[n][[;; , 2]]] > 2; seq[kmax_] := Module[{s = {}, k1 = 1, gapmax = 0, gap}, Do[If[cubQ[k], gap = k - k1; If[gap > gapmax, gapmax = gap; AppendTo[s, k1]]; k1 = k], {k, 2, kmax}]; s]; seq[10^6]
  • PARI
    iscubefull(n) = n==1 || vecmin(factor(n)[, 2]) > 2;
    lista(kmax) = {my(gapmax = 0, gap, k1 = 1); for(k = 2, kmax, if(iscubefull(k), gap = k - k1; if(gap > gapmax, gapmax = gap; print1(k1, ", ")); k1 = k));}

A307703 Highly powerful numbers (A005934) that are not cubeful (A036966).

Original entry on oeis.org

4, 144, 288, 86400, 129600, 194400, 259200, 518400, 190512000, 317520000, 381024000, 635040000, 9681819840000, 215982036990720000, 9466852651364908800000, 14200278977047363200000, 28400557954094726400000, 174294224164279335916800000, 522882672492838007750400000
Offset: 1

Views

Author

Amiram Eldar, Apr 22 2019

Keywords

Comments

Lacampagne and Selfridge proved that these are the only terms.
The positions of the terms in A005934 are 2, 8, 10, 25, 27, 28, 30, 33, 55, 58, 60, 62, 107, 161, 230, 234, 240, 302, 315.

Crossrefs

Programs

  • Mathematica
    pmax = 1; s = {}; Do[e = FactorInteger[n][[;; , 2]]; p = Times @@ e; If[p > pmax, pmax = p; If[Min[e] < 3, AppendTo[s, n]]], {n, 2, 10^6}]; s

A030078 Cubes of primes.

Original entry on oeis.org

8, 27, 125, 343, 1331, 2197, 4913, 6859, 12167, 24389, 29791, 50653, 68921, 79507, 103823, 148877, 205379, 226981, 300763, 357911, 389017, 493039, 571787, 704969, 912673, 1030301, 1092727, 1225043, 1295029, 1442897, 2048383, 2248091, 2571353, 2685619, 3307949
Offset: 1

Views

Author

Keywords

Comments

Numbers with exactly three factorizations: A001055(a(n)) = 3 (e.g., a(4) = 1*343 = 7*49 = 7*7*7). - Reinhard Zumkeller, Dec 29 2001
Intersection of A014612 and A000578. Intersection of A014612 and A030513. - Wesley Ivan Hurt, Sep 10 2013
Let r(n) = (a(n)-1)/(a(n)+1) if a(n) mod 4 = 1, (a(n)+1)/(a(n)-1) otherwise; then Product_{n>=1} r(n) = (9/7) * (28/26) * (124/126) * (344/342) * (1332/1330) * ... = 48/35. - Dimitris Valianatos, Mar 06 2020
There exist 5 groups of order p^3, when p prime, so this is a subsequence of A054397. Three of them are abelian: C_p^3, C_p^2 X C_p and C_p X C_p X C_p = (C_p)^3. For 8 = 2^3, the 2 nonabelian groups are D_8 and Q_8; for odd prime p, the 2 nonabelian groups are (C_p x C_p) : C_p, and C_p^2 : C_p (remark, for p = 2, these two semi-direct products are isomorphic to D_8). Here C, D, Q mean Cyclic, Dihedral, Quaternion groups of the stated order; the symbols X and : mean direct and semidirect products respectively. - Bernard Schott, Dec 11 2021

Examples

			a(3) = 125; since the 3rd prime is 5, a(3) = 5^3 = 125.
		

References

  • Edmund Landau, Elementary Number Theory, translation by Jacob E. Goodman of Elementare Zahlentheorie (Vol. I_1 (1927) of Vorlesungen über Zahlentheorie), by Edmund Landau, with added exercises by Paul T. Bateman and E. E. Kohlbecker, Chelsea Publishing Co., New York, 1958, pp. 31-32.

Crossrefs

Other sequences that are k-th powers of primes are: A000040 (k=1), A001248 (k=2), this sequence (k=3), A030514 (k=4), A050997 (k=5), A030516 (k=6), A092759 (k=7), A179645 (k=8), A179665 (k=9), A030629 (k=10), A079395 (k=11), A030631 (k=12), A138031 (k=13), A030635 (k=16), A138032 (k=17), A030637 (k=18).
Cf. A060800, A131991, A000578, subsequence of A046099.
Subsequence of A007422 and of A054397.

Programs

Formula

n such that A062799(n) = 3. - Benoit Cloitre, Apr 06 2002
a(n) = A000040(n)^3. - Omar E. Pol, Jul 27 2009
A064380(a(n)) = A000010(a(n)). - Vladimir Shevelev, Apr 19 2010
A003415(a(n)) = A079705(n). - Reinhard Zumkeller, Jun 26 2011
A056595(a(n)) = 2. - Reinhard Zumkeller, Aug 15 2011
A000005(a(n)) = 4. - Wesley Ivan Hurt, Sep 10 2013
a(n) = A119959(n) * A008864(n) -1.- R. J. Mathar, Aug 13 2019
Sum_{n>=1} 1/a(n) = P(3) = 0.1747626392... (A085541). - Amiram Eldar, Jul 27 2020
From Amiram Eldar, Jan 23 2021: (Start)
Product_{n>=1} (1 + 1/a(n)) = zeta(3)/zeta(6) (A157289).
Product_{n>=1} (1 - 1/a(n)) = 1/zeta(3) (A088453). (End)

A046099 Numbers that are not cubefree. Numbers divisible by a cube greater than 1. Complement of A004709.

Original entry on oeis.org

8, 16, 24, 27, 32, 40, 48, 54, 56, 64, 72, 80, 81, 88, 96, 104, 108, 112, 120, 125, 128, 135, 136, 144, 152, 160, 162, 168, 176, 184, 189, 192, 200, 208, 216, 224, 232, 240, 243, 248, 250, 256, 264, 270, 272, 280, 288, 296, 297, 304, 312, 320, 324, 328, 336
Offset: 1

Views

Author

Keywords

Comments

Also called cubeful numbers, but this term is ambiguous and is best avoided.
Numbers n such that A007427(n) = sum(d|n,mu(d)*mu(n/d)) == 0. - Benoit Cloitre, Apr 17 2002
The convention in the OEIS is that squareful, cubeful, biquadrateful (A046101), ... mean the same as "not squarefree" etc., while 2- or square-full, 3- or cube-full (A036966), 4-full (A036967) are used for Golomb's notion of powerful numbers (A001694, see references there), when each prime factor occurs to a power > 1. - M. F. Hasler, Feb 12 2008. Added by N. J. A. Sloane, Apr 25 2023: This suggestion has not been a success. It is hopeless to try to make a distinction between "cubeful" and "cubefull". To avoid ambiguity, do not use either term, but instead say exactly what you mean.
Also solutions to equation tau_{-2}(n)=0, where tau_{-2} is A007427. - Enrique Pérez Herrero, Jan 19 2013
The asymptotic density of this sequence is 1 - 1/zeta(3) = 0.168092... - Amiram Eldar, Jul 09 2020

Crossrefs

Complement of A004709.
Subsequences: A000578 and A030078.

Programs

  • Haskell
    a046099 n = a046099_list !! (n-1)
    a046099_list = filter ((== 1) . a212793) [1..]
    -- Reinhard Zumkeller, May 27 2012
    
  • Maple
    isA046099 := proc(n)
        local p;
        for p in ifactors(n)[2] do
            if op(2,p) >= 3 then
                return true;
            end if;
        end do:
        false ;
    end proc:
    for n from 1 do
        if isA046099(n) then
            printf("%d\n",n) ;
        end if;
    end do: # R. J. Mathar, Dec 08 2015
  • Mathematica
    lst={};Do[a=0;Do[If[FactorInteger[m][[n, 2]]>2, a=1], {n, Length[FactorInteger[m]]}];If[a==1, AppendTo[lst, m]], {m, 10^3}];lst (* Vladimir Joseph Stephan Orlovsky, Aug 15 2008 *)
  • PARI
    is(n)=n>7 && vecmax(factor(n)[,2])>2 \\ Charles R Greathouse IV, Sep 17 2015
    
  • Python
    from sympy.ntheory.factor_ import core
    def ok(n): return core(n, 3) != n
    print(list(filter(ok, range(1, 337)))) # Michael S. Branicky, Aug 16 2021
    
  • Python
    from sympy import mobius, integer_nthroot
    def A046099(n):
        def f(x): return n+sum(mobius(k)*(x//k**3) for k in range(1, integer_nthroot(x,3)[0]+1))
        m, k = n, f(n)
        while m != k:
            m, k = k, f(k)
        return m # Chai Wah Wu, Aug 05 2024

Formula

A212793(a(n)) = 0. - Reinhard Zumkeller, May 27 2012
Sum_{n>=1} 1/a(n)^s = (zeta(s)*(zeta(3*s)-1))/zeta(3*s). - Amiram Eldar, Dec 27 2022

Extensions

More terms from Vladimir Joseph Stephan Orlovsky, Aug 15 2008
Edited by N. J. A. Sloane, Jul 27 2009

A076467 Perfect powers m^k where m is a positive integer and k >= 3.

Original entry on oeis.org

1, 8, 16, 27, 32, 64, 81, 125, 128, 216, 243, 256, 343, 512, 625, 729, 1000, 1024, 1296, 1331, 1728, 2048, 2187, 2197, 2401, 2744, 3125, 3375, 4096, 4913, 5832, 6561, 6859, 7776, 8000, 8192, 9261, 10000, 10648, 12167, 13824, 14641, 15625, 16384, 16807
Offset: 1

Views

Author

Robert G. Wilson v, Oct 14 2002

Keywords

Comments

If p|n with p prime then p^3|n.

Crossrefs

Subsequence of A036966.

Programs

  • Haskell
    a076467 n = a076467_list !! (n-1)
    a076467_list = 1 : filter ((> 2) . foldl1 gcd . a124010_row) [2..]
    -- Reinhard Zumkeller, Apr 13 2012
    
  • Haskell
    import qualified Data.Set as Set (null)
    import Data.Set (empty, insert, deleteFindMin)
    a076467 n = a076467_list !! (n-1)
    a076467_list = 1 : f [2..] empty where
       f xs'@(x:xs) s | Set.null s || m > x ^ 3 = f xs $ insert (x ^ 3, x) s
                      | m == x ^ 3  = f xs s
                      | otherwise = m : f xs' (insert (m * b, b) s')
                      where ((m, b), s') = deleteFindMin s
    -- Reinhard Zumkeller, Jun 18 2013
    
  • Maple
    N:= 10^5: # to get all terms <= N
    S:= {1, seq(seq(m^k, m = 2 .. floor(N^(1/k))),k=3..ilog2(N))}:
    sort(convert(S,list)); # Robert Israel, Sep 30 2015
  • Mathematica
    a = {1}; Do[ If[ Apply[ GCD, Last[ Transpose[ FactorInteger[n]]]] > 2, a = Append[a, n]; Print[n]], {n, 2, 17575}]; a
    (* Second program: *)
    n = 10^5; Join[{1}, Table[m^k, {k, 3, Floor[Log[2, n]]}, {m, 2, Floor[n^(1/k)]}] // Flatten // Union] (* Jean-François Alcover, Feb 13 2018, after Robert Israel *)
  • PARI
    is(n)=ispower(n)>2||n==1 \\ Charles R Greathouse IV, Sep 03 2015, edited for n=1 by M. F. Hasler, May 26 2018
    
  • PARI
    A076467(lim)={my(L=List(1),lim2=logint(lim,2),m,k);for(k=3,lim2, for(m=2,sqrtnint(lim,k),listput(L, m^k);));listsort(L,1);L}
    b076467(lim)={my(L=A076467(lim)); for(i=1,#L,print(i ," ",L[i]));} \\ Anatoly E. Voevudko, Sep 29 2015, edited by M. F. Hasler, May 25 2018
    
  • PARI
    A076467_vec(LIM,S=List(1))={for(x=2,sqrtnint(LIM,3),for(k=3, logint(LIM, x), listput(S, x^k))); Set(S)} \\ M. F. Hasler, May 25 2018
    
  • Python
    from sympy import mobius, integer_nthroot
    def A076467(n):
        def f(x): return int(n-1+x-integer_nthroot(x,4)[0]+sum(mobius(k)*(integer_nthroot(x,k)[0]+integer_nthroot(x,k<<1)[0]-2) for k in range(3,x.bit_length())))
        kmin, kmax = 1,2
        while f(kmax) >= kmax:
            kmax <<= 1
        while True:
            kmid = kmax+kmin>>1
            if f(kmid) < kmid:
                kmax = kmid
            else:
                kmin = kmid
            if kmax-kmin <= 1:
                break
        return kmax # Chai Wah Wu, Aug 14 2024

Formula

For n > 1: GCD(exponents in prime factorization of a(n)) > 2, cf. A124010. - Reinhard Zumkeller, Apr 13 2012
Sum_{n>=1} 1/a(n) = 2 - zeta(2) + Sum_{k>=2} mu(k)*(2 - zeta(k) - zeta(2*k)) = 1.3300056287... - Amiram Eldar, Jul 02 2022

Extensions

Edited by Robert Israel, Sep 30 2015

A023052 Perfect Digital Invariants: numbers that are the sum of some fixed power of their digits.

Original entry on oeis.org

0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 153, 370, 371, 407, 1634, 4150, 4151, 8208, 9474, 54748, 92727, 93084, 194979, 548834, 1741725, 4210818, 9800817, 9926315, 14459929, 24678050, 24678051, 88593477, 146511208, 472335975, 534494836, 912985153
Offset: 1

Views

Author

Keywords

Comments

The old name was "Powerful numbers, definition (3)". Cf. A001694, A007532. - N. J. A. Sloane, Jan 16 2022.
Randle has suggested that these numbers be called "powerful", but this usually refers to a distinct property related to prime factorization, cf. A001694, A036966, A005934.
Numbers m such that m = Sum_{i=1..k} d(i)^s for some s, where d(1..k) are the decimal digits of m.
Superset of A005188 (Plusperfect, narcissistic or Armstrong numbers: s=k), A046197 (s=3), A052455 (s=4), A052464 (s=5), A124068 (s=6, 7), A124069 (s=8). - R. J. Mathar, Jun 15 2009, Jun 22 2009

Examples

			153 = 1^3 + 5^3 + 3^3, 4210818 = 4^7 + 2^7 + 1^7 + 0^7 + 8^7 + 1^7 + 8^7.
		

Crossrefs

Cf. A001694 (powerful numbers: p|n => p^2|n), A005934 (highly powerful numbers).
Cf. A005188 (here the power must be equal to the number of digits).
In other bases: A162216 (base 3), A162219 (base 4), A162222 (base 5), A162225 (base 6), A162228 (base 7), A162231 (base 8), A162234 (base 9).

Programs

  • Mathematica
    Select[Range[0, 10^5], Function[m, AnyTrue[Function[k, Total@ Map[Power[#, k] &, IntegerDigits@ m]] /@ Range@ 10, # == m &]]] (* Michael De Vlieger, Feb 08 2016, Version 10 *)
  • PARI
    is(n)=if(n<10, return(1)); my(d=digits(n),m=vecmax(d)); if(m<2, return(0)); for(k=3,logint(n,m), if(sum(i=1,#d,d[i]^k)==n, return(1))); 0 \\ Charles R Greathouse IV, Feb 06 2017
    
  • PARI
    select( is_A023052(n,b=10)={nn|| return(t==n))}, [0..10^5]) \\  M. F. Hasler, Nov 21 2019

Extensions

Computed to 10^50 by G. N. Gusev (GGN(AT)rm.yaroslavl.ru)
Computed to 10^74 by Xiaoqing Tang
A-number typo corrected by R. J. Mathar, Jun 22 2009
Computed to 10^105 by Joseph Myers
Cross-references edited by Joseph Myers, Jun 28 2009
Edited by M. F. Hasler, Nov 21 2019
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