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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A001160 sigma_5(n), the sum of the 5th powers of the divisors of n.

Original entry on oeis.org

1, 33, 244, 1057, 3126, 8052, 16808, 33825, 59293, 103158, 161052, 257908, 371294, 554664, 762744, 1082401, 1419858, 1956669, 2476100, 3304182, 4101152, 5314716, 6436344, 8253300, 9768751, 12252702, 14408200, 17766056, 20511150
Offset: 1

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Keywords

Comments

If the canonical factorization of n into prime powers is the product of p^e(p) then sigma_k(n) = Product_p ((p^((e(p)+1)*k))-1)/(p^k-1).
Sum_{d|n} 1/d^k is equal to sigma_k(n)/n^k. So sequences A017665-A017712 also give the numerators and denominators of sigma_k(n)/n^k for k = 1..24. The power sums sigma_k(n) are in sequences A000203 (k=1), A001157-A001160 (k=2,3,4,5), A013954-A013972 for k = 6,7,...,24. - Ahmed Fares (ahmedfares(AT)my-deja.com), Apr 05 2001
Empirical: Sum_{n>=1} a(n)/exp(2*Pi*n) = 1/504. - Simon Plouffe, Mar 01 2021

References

  • M. Abramowitz and I. A. Stegun, eds., Handbook of Mathematical Functions, National Bureau of Standards Applied Math.Series 55, Tenth Printing, 1972, p. 827.
  • G. H. Hardy, Ramanujan: twelve lectures on subjects suggested by his life and work, AMS Chelsea Publishing, Providence, Rhode Island, 2002, p. 166.
  • N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
  • N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
  • Zagier, Don. "Elliptic modular forms and their applications." The 1-2-3 of modular forms. Springer Berlin Heidelberg, 2008. 1-103. See p. 17, G_6(z).

Crossrefs

Cf. A000005, A000203, A001157, A001158, A001159, A013973, A000584 (Mobius transform), A178448 (Dirichlet inverse)

Programs

Formula

Multiplicative with a(p^e) = (p^(5e+5)-1)/(p^5-1). - David W. Wilson, Aug 01 2001
G.f.: sum(k>=1, k^5*x^k/(1-x^k)). - Benoit Cloitre, Apr 21 2003
Dirichlet g.f.: zeta(s)*zeta(s-5). - R. J. Mathar, Mar 06 2011
G.f. also (1 - E_6(q))/540, with the g.f. E_6 of A013973. See Hardy p. 166, (10.5.7) with R = E_6. - Wolfdieter Lang, Jan 31 2017
L.g.f.: -log(Product_{k>=1} (1 - x^k)^(k^4)) = Sum_{n>=1} a(n)*x^n/n. - Ilya Gutkovskiy, May 06 2017
a(n) = Sum_{1 <= i, j, k, l, m <= n} tau(gcd(i, j, k, l, m, n)) = Sum_{d divides n} tau(d) * J_5(n/d), where the divisor function tau(n) = A000005(n) and the Jordan totient function J_5(n) = A059378(n). - Peter Bala, Jan 22 2024

A268335 Exponentially odd numbers.

Original entry on oeis.org

1, 2, 3, 5, 6, 7, 8, 10, 11, 13, 14, 15, 17, 19, 21, 22, 23, 24, 26, 27, 29, 30, 31, 32, 33, 34, 35, 37, 38, 39, 40, 41, 42, 43, 46, 47, 51, 53, 54, 55, 56, 57, 58, 59, 61, 62, 65, 66, 67, 69, 70, 71, 73, 74, 77, 78, 79, 82, 83, 85, 86, 87, 88, 89, 91, 93, 94, 95, 96, 97
Offset: 1

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Author

Vladimir Shevelev, Feb 01 2016

Keywords

Comments

The sequence is formed by 1 and the numbers whose prime power factorization contains only odd exponents.
The density of the sequence is the constant given by A065463.
Except for the first term the same as A002035. - R. J. Mathar, Feb 07 2016
Also numbers k all of whose divisors are bi-unitary divisors (i.e., A286324(k) = A000005(k)). - Amiram Eldar, Dec 19 2018
The term "exponentially odd integers" was apparently coined by Cohen (1960). These numbers were also called "unitarily 2-free", or "2-skew", by Cohen (1961). - Amiram Eldar, Jan 22 2024

Crossrefs

Programs

  • Mathematica
    Select[Range@ 100, AllTrue[Last /@ FactorInteger@ #, OddQ] &] (* Version 10, or *)
    Select[Range@ 100, Times @@ Boole[OddQ /@ Last /@ FactorInteger@ #] == 1 &] (* Michael De Vlieger, Feb 02 2016 *)
  • PARI
    isok(n)=my(f = factor(n)); for (k=1, #f~, if (!(f[k,2] % 2), return (0))); 1; \\ Michel Marcus, Feb 02 2016
    
  • Python
    from itertools import count, islice
    from sympy import factorint
    def A268335_gen(startvalue=1): # generator of terms >= startvalue
        return filter(lambda n:all(e&1 for e in factorint(n).values()),count(max(startvalue,1)))
    A268335_list = list(islice(A268335_gen(),20)) # Chai Wah Wu, Jun 22 2023

Formula

Sum_{a(n)<=x} 1 = C*x + O(sqrt(x)*log x*e^(c*sqrt(log x)/(log(log x))), where c = 4*sqrt(2.4/log 2) = 7.44308... and C = Product_{prime p} (1 - 1/p*(p + 1)) = 0.7044422009991... (A065463).
Sum_{n>=1} 1/a(n)^s = zeta(2*s) * Product_{p prime} (1 + 1/p^s - 1/p^(2*s)), s>1. - Amiram Eldar, Sep 26 2023

A001015 Seventh powers: a(n) = n^7.

Original entry on oeis.org

0, 1, 128, 2187, 16384, 78125, 279936, 823543, 2097152, 4782969, 10000000, 19487171, 35831808, 62748517, 105413504, 170859375, 268435456, 410338673, 612220032, 893871739, 1280000000, 1801088541, 2494357888, 3404825447, 4586471424, 6103515625, 8031810176
Offset: 0

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Comments

For n>0, (a(3*n-1)^7-a(2*n-1)^7-a(n)^7)/(7*(3*n-1)*(2*n-1)*n) = (2*A001106(n)+1)^2 (see Barisien reference, problem 173). - Bruno Berselli, Feb 01 2011
Number of the form a(n) + a(n+1) + ... + a(n+k) is never prime for all n, k>=0. This could be proved by the method indicated in the comment in A256581. - Vladimir Shevelev and Peter J. C. Moses, Apr 04 2015

References

  • E.-N. Barisien, Supplemento al Periodico di Matematica, Raffaello Giusti Editore (Livorno), July 1913, p. 135 (Problem 173).
  • N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
  • N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Crossrefs

Cf. A000584 (5th powers), A013665 (zeta(7)), A275710 (eta(7)), A300785.
Cf. A003369 - A003379 (sums of 2, ..., 12 positive seventh powers).

Programs

Formula

Multiplicative with a(p^e) = p^(7e). - David W. Wilson, Aug 01 2001
Totally multiplicative sequence with a(p) = p^7 for primes p. - Jaroslav Krizek, Nov 01 2009
a(n) = 7*a(n-1) - 21* a(n-2) + 35*a(n-3) - 35*a(n-4) + 21*a(n-5) - 7*a(n-6) + a(n-7) + 5040. - Ant King, Sep 24 2013
a(n) = n + Sum_{j=0..n-1}{k=1..6}binomial(7,k)*j^(7-k). - Patrick J. McNab, Mar 28 2016
G.f.: x*(1+120*x+1191*x^2+2416*x^3+1191*x^4+120*x^5+x^6)/(1-x)^8. See the Maple program. - Wolfdieter Lang, Oct 14 2016
From Kolosov Petro, Oct 22 2018: (Start)
a(n) = Sum_{k=1..n} A300785(n,k).
a(n) = Sum_{k=0..n-1} A300785(n,k). (End)
From Amiram Eldar, Oct 08 2020: (Start)
Sum_{n>=1} 1/a(n) = zeta(7) (A013665).
Sum_{n>=1} (-1)^(n+1)/a(n) = 63*zeta(7)/64 (A275710). (End)

Extensions

More terms from James Sellers, Sep 19 2000

A000539 Sum of 5th powers: 0^5 + 1^5 + 2^5 + ... + n^5.

Original entry on oeis.org

0, 1, 33, 276, 1300, 4425, 12201, 29008, 61776, 120825, 220825, 381876, 630708, 1002001, 1539825, 2299200, 3347776, 4767633, 6657201, 9133300, 12333300, 16417401, 21571033, 28007376, 35970000, 45735625, 57617001, 71965908, 89176276, 109687425, 133987425, 162616576
Offset: 0

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Comments

This sequence is related to A000538 by a(n) = n*A000538(n) - Sum_{i=0..n-1} A000538(i). - Bruno Berselli, Apr 26 2010
See comment in A008292 for a formula for r-th successive summation of Sum_{k=1..n} k^j. - Gary Detlefs, Jan 02 2014

References

  • M. Abramowitz and I. A. Stegun, eds., Handbook of Mathematical Functions, National Bureau of Standards Applied Math. Series 55, 1964 (and various reprintings), p. 813.
  • L. Comtet, Advanced Combinatorics, Reidel, 1974, p. 155.
  • R. L. Graham, D. E. Knuth and O. Patashnik, Concrete Mathematics. Addison-Wesley, Reading, MA, 1991, p. 275.
  • N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
  • N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Crossrefs

Partial sums of A000584. Row 5 of array A103438.

Programs

  • Magma
    [n^2*(n+1)^2*(2*n^2+2*n-1)/12: n in [0..30]]; // Vincenzo Librandi, Apr 04 2015
    
  • Maple
    A000539:=-(1+26*z+66*z**2+26*z**3+z**4)/(z-1)**7; # Simon Plouffe in his 1992 dissertation
    a[0]:=0:a[1]:=1:for n from 2 to 50 do a[n]:=a[n-1]+n^5 od: seq(a[n], n=0..30); # Zerinvary Lajos, Feb 22 2008
    a:=n->sum(j^5,j=0..n): seq(a(n), n=0..30); # Zerinvary Lajos, Jun 05 2008
  • Mathematica
    Accumulate[Range[0, 40]^5]
    LinearRecurrence[{7, -21, 35, -35, 21, -7, 1}, {0, 1, 33, 276, 1300, 4425, 12201}, 41] (* Jean-François Alcover, Feb 09 2016 *)
  • Maxima
    A000539(n):=n^2*(n+1)^2*(2*n^2+2*n-1)/12$ makelist(A000539(n),n,0,30); /* Martin Ettl, Nov 12 2012 */
    
  • PARI
    a(n)=n^2*(n+1)^2*(2*n^2+2*n-1)/12 \\ Charles R Greathouse IV, Jul 15 2011
    
  • PARI
    concat(0, Vec(x*(1+26*x+66*x^2+26*x^3+x^4)/(1-x)^7 + O(x^100))) \\ Altug Alkan, Dec 07 2015
    
  • Python
    A000539_list, m = [0], [120, -240, 150, -30, 1, 0, 0]
    for _ in range(10**2):
        for i in range(6):
            m[i+1] += m[i]
        A000539_list.append(m[-1]) # Chai Wah Wu, Nov 05 2014
    
  • Python
    def A000539(n): return n**2*(n**2*(n*(n+3<<1)+5)-1)//12 # Chai Wah Wu, Oct 03 2024

Formula

a(n) = n^2*(n+1)^2*(2*n^2+2*n-1)/12.
a(n) = sqrt(Sum_{j=1..n}Sum_{i=1..n}(i*j)^5). - Alexander Adamchuk, Oct 26 2004
a(n) = Sum_{i = 1..n} J_5(i)*floor(n/i), where J_5 is A059378. - Enrique Pérez Herrero, Feb 26 2012
a(n) = 6*a(n-1) - 15* a(n-2) + 20*a(n-3) - 15*a(n-4) + 6*a(n-5) - a(n-6) + 120. - Ant King, Sep 23 2013
a(n) = 120*C(n+3,6) + 30*C(n+2,4) + C(n+1,2) (Knuth). - Gary Detlefs, Jan 02 2014
a(n) = -Sum_{j=1..5} j*Stirling1(n+1,n+1-j)*Stirling2(n+5-j,n). - Mircea Merca, Jan 25 2014
Sum_{n>=1} 1/a(n) = 60 - 4*Pi^2 + 8*sqrt(3)*Pi * tan(sqrt(3)*Pi/2). - Vaclav Kotesovec, Feb 13 2015
a(n) = (n + 1)^2*n^2*(n + 1/2 + sqrt(3/4))*(n + 1/2 - sqrt(3/4))/6. See the Graham et al. reference, p. 275. - Wolfdieter Lang, Apr 02 2015
G.f.: x*(1+26*x+66*x^2+26*x^3+x^4)/(1-x)^7. - Robert Israel, Dec 07 2015
a(n) = (4/3)*A000217(n)^3 - (1/3)*A000217(n)^2. - Michael Raney, Feb 19 2016
a(n) = (binomial(n+1,4) + 6*binomial(n+2,4) + binomial(n+3,4))*(binomial(n+2,3) - binomial(n+1,3)). - Tony Foster III, Oct 21 2018
a(n) = 24*A006542(n+2) + A000537(n). - Yasser Arath Chavez Reyes, May 04 2024
E.g.f.: exp(x)*x*(12 + 186*x + 360*x^2 + 195*x^3 + 36*x^4 + 2*x^5)/12. - Stefano Spezia, May 04 2024

A003347 Numbers that are the sum of 2 positive 5th powers.

Original entry on oeis.org

2, 33, 64, 244, 275, 486, 1025, 1056, 1267, 2048, 3126, 3157, 3368, 4149, 6250, 7777, 7808, 8019, 8800, 10901, 15552, 16808, 16839, 17050, 17831, 19932, 24583, 32769, 32800, 33011, 33614, 33792, 35893, 40544, 49575, 59050, 59081, 59292, 60073, 62174, 65536, 66825, 75856
Offset: 1

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Examples

			From _David A. Corneth_, Aug 03 2020: (Start)
917552689 is in the sequence as 917552689 = 17^5 + 62^5.
2557575000 is in the sequence as 2557575000 = 45^5 + 75^5.
5828050944 is in the sequence as 5828050944 = 56^5 + 88^5. (End)
		

Crossrefs

Programs

A003350 Numbers that are the sum of 5 positive 5th powers.

Original entry on oeis.org

5, 36, 67, 98, 129, 160, 247, 278, 309, 340, 371, 489, 520, 551, 582, 731, 762, 793, 973, 1004, 1028, 1059, 1090, 1121, 1152, 1215, 1270, 1301, 1332, 1363, 1512, 1543, 1574, 1754, 1785, 1996, 2051, 2082, 2113, 2144, 2293, 2324, 2355, 2535, 2566, 2777, 3074, 3105, 3129
Offset: 1

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Examples

			From _David A. Corneth_, Aug 03 2020: (Start)
122490 is in the sequence as 122490 = 3^5 + 4^5 + 5^5 + 9^5 + 9^5.
251124 is in the sequence as 251124 = 1^5 + 3^5 + 4^5 + 4^5 + 12^5.
349858 is in the sequence as 349858 = 1^5 + 1^5 + 4^5 + 10^5 + 12^5. (End)
		

Crossrefs

Programs

  • Mathematica
    f[upto_]:=Module[{max=Floor[Power[upto, (5)^-1]],tp},tp=Union[ Total/@ (Tuples[ Range[max],{5}]^5)]; Select[tp,#<=upto&]]; f[2100]  (* Harvey P. Dale, Mar 22 2011 *)

A003349 Numbers that are the sum of 4 positive 5th powers.

Original entry on oeis.org

4, 35, 66, 97, 128, 246, 277, 308, 339, 488, 519, 550, 730, 761, 972, 1027, 1058, 1089, 1120, 1269, 1300, 1331, 1511, 1542, 1753, 2050, 2081, 2112, 2292, 2323, 2534, 3073, 3104, 3128, 3159, 3190, 3221, 3315, 3370, 3401, 3432, 3612, 3643, 3854, 4096, 4151, 4182, 4213
Offset: 1

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Examples

			From _David A. Corneth_, Aug 03 2020: (Start)
670593 is in the sequence as 670593 = 1^5 + 8^5 + 10^5 + 14^5.
862512 is in the sequence as 862512 = 7^5 + 9^5 + 12^5 + 14^5.
1892695 is in the sequence as 1892695 = 1^5 + 1^5 + 5^5 + 18^5. (End)
		

Crossrefs

Programs

  • Mathematica
    f@n_:= Select[Range@n,IntegerPartitions[#,{4},Range@(n^(1/5))^5] != {} &]; f@10000 (* Hans Rudolf Widmer, Dec 04 2022 *)

Extensions

Incorrect program removed by David A. Corneth, Aug 03 2020

A003351 Numbers that are the sum of 6 positive 5th powers.

Original entry on oeis.org

6, 37, 68, 99, 130, 161, 192, 248, 279, 310, 341, 372, 403, 490, 521, 552, 583, 614, 732, 763, 794, 825, 974, 1005, 1029, 1036, 1060, 1091, 1122, 1153, 1184, 1216, 1247, 1271, 1302, 1333, 1364, 1395, 1458, 1513, 1544, 1575, 1606, 1755, 1786, 1817, 1997, 2028, 2052
Offset: 1

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Examples

			From _David A. Corneth_, Aug 03 2020: (Start)
90185 is in the sequence as 90185 = 2^5 + 6^5 + 6^5 + 6^5 + 6^5 + 9^5.
104636 is in the sequence as 104636 = 1^5 + 3^5 + 3^5 + 4^5 + 5^5 + 10^5.
151173 is in the sequence as 151173 = 2^5 + 2^5 + 3^5 + 8^5 + 9^5 + 9^5. (End)
		

Crossrefs

A003352 Numbers that are the sum of 7 positive 5th powers.

Original entry on oeis.org

7, 38, 69, 100, 131, 162, 193, 224, 249, 280, 311, 342, 373, 404, 435, 491, 522, 553, 584, 615, 646, 733, 764, 795, 826, 857, 975, 1006, 1030, 1037, 1061, 1068, 1092, 1123, 1154, 1185, 1216, 1217, 1248, 1272
Offset: 1

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Examples

			From _David A. Corneth_, Aug 03 2020: (Start)
41940 is in the sequence as 41940 = 2^5 + 2^5 + 3^5 + 3^5 + 6^5 + 7^5 + 7^5.
65614 is in the sequence as 65614 = 1^5 + 3^5 + 3^5 + 6^5 + 6^5 + 7^5 + 8^5.
96845 is in the sequence as 96845 = 1^5 + 2^5 + 4^5 + 5^5 + 7^5 + 7^5 + 9^5. (End)
		

Crossrefs

Extensions

Incorrect program removed by David A. Corneth, Aug 03 2020

A003353 Numbers that are the sum of 8 positive 5th powers.

Original entry on oeis.org

8, 39, 70, 101, 132, 163, 194, 225, 250, 256, 281, 312, 343, 374, 405, 436, 467, 492, 523, 554, 585, 616, 647, 678, 734, 765, 796, 827, 858, 889, 976, 1007, 1031, 1038, 1062, 1069, 1093, 1100, 1124, 1155, 1186, 1217, 1218, 1248, 1249, 1273, 1280, 1304, 1311, 1335, 1366
Offset: 1

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Examples

			From _David A. Corneth_, Aug 03 2020: (Start)
32373 is in the sequence as 32373 = 1^5 + 1^5 + 3^5 + 4^5 + 6^5 + 6^5 + 6^5 + 6^5.
42605 is in the sequence as 42605 = 3^5 + 3^5 + 3^5 + 3^5 + 3^5 + 6^5 + 7^5 + 7^5.
58030 is in the sequence as 58030 = 2^5 + 2^5 + 4^5 + 6^5 + 6^5 + 6^5 + 7^5 + 7^5. (End)
		

Crossrefs

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