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 1-9 of 9 results.

A019284 Let sigma_m (n) be result of applying sum-of-divisors function m times to n; call n (m,k)-perfect if sigma_m (n) = k*n; sequence gives the (2,7)-perfect numbers.

Original entry on oeis.org

24, 1536, 47360, 343976, 572941926400
Offset: 1

Views

Author

N. J. A. Sloane

Keywords

Comments

See also the Cohen-te Riele links under A019276.
No other terms < 5*10^11. - Jud McCranie, Feb 08 2012
572941926400 is also a term. See comment in A019278. - Michel Marcus, May 15 2016
a(6) > 4*10^12, if it exists. - Giovanni Resta, Feb 26 2020

Links

Crossrefs

Cf. A000668, A019278, A019279, A019281, A019282, A019283, A019285, A019286, A019287, A019288, A019289, A019290, A019291.

Programs

  • Mathematica
    Select[Range[50000], DivisorSigma[1, DivisorSigma[1, #]]/# == 7 &] (* Robert Price, Apr 07 2019 *)
  • PARI
    isok(n) = sigma(sigma(n))/n  == 7; \\ Michel Marcus, May 12 2016

Extensions

a(5) from Giovanni Resta, Feb 26 2020

A019281 Let sigma_m (n) be result of applying sum-of-divisors function m times to n; call n (m,k)-perfect if sigma_m (n) = k*n; sequence gives the (2,3)-perfect numbers.

Original entry on oeis.org

8, 21, 512
Offset: 1

Views

Author

N. J. A. Sloane

Keywords

Comments

See also the Cohen-te Riele links under A019276.
No further term < 10^9 [see Table 1].
No other terms < 5*10^11. - Jud McCranie, Feb 08 2012
a(4) > 4*10^12, if it exists. - Giovanni Resta, Feb 26 2020

Links

Crossrefs

Cf. A019278, A019279, A019282, A019283, A019284, A019285, A019286, A019287, A019288, A019289, A019290, A019291.

A019282 Let sigma_m (n) be result of applying sum-of-divisors function m times to n; call n (m,k)-perfect if sigma_m (n) = k*n; sequence gives the (2,4)-perfect numbers.

Original entry on oeis.org

15, 1023, 29127, 355744082763
Offset: 1

Views

Author

N. J. A. Sloane

Keywords

Comments

See also the Cohen-te Riele links under A019276.
No other terms < 5*10^11. - Jud McCranie, Feb 08 2012
a(5) > 4*10^12, if it exists. - Giovanni Resta, Feb 26 2020

Links

Crossrefs

Cf. A019278, A019279, A019281, A019283, A019284, A019285, A019286, A019287, A019288, A019289, A019290, A019291.

Programs

  • Mathematica
    Select[Range[100000], DivisorSigma[1, DivisorSigma[1, #]]/# == 4 &] (* Robert Price, Apr 07 2019 *)
  • PARI
    isok(n) = sigma(sigma(n))/n  == 4; \\ Michel Marcus, May 12 2016

Extensions

a(4) from Jud McCranie, Feb 08 2012

A019286 Let sigma_m (n) be result of applying sum-of-divisors function m times to n; call n (m,k)-perfect if sigma_m (n) = k*n; sequence gives the (2,9)-perfect numbers.

Original entry on oeis.org

168, 10752, 331520, 691200, 1556480, 1612800, 106151936, 5099962368, 4010593484800
Offset: 1

Views

Author

N. J. A. Sloane

Keywords

Comments

See also the Cohen-te Riele links under A019276.
No other terms < 5*10^11. - Jud McCranie, Feb 08 2012
4010593484800 is also a term. See comment in A019278. - Michel Marcus, May 15 2016

Links

Crossrefs

Cf. A000668, A019278, A019279, A019281, A019282, A019283, A019284, A019285, A019286, A019287, A019288, A019289, A019290, A019291.

Programs

  • PARI
    isok(n) = sigma(sigma(n))/n  == 9; \\ Michel Marcus, May 12 2016

Extensions

a(8) by Jud McCranie, Jan 28 2012
a(9) from Giovanni Resta, Feb 26 2020

A019287 Let sigma_m (n) be result of applying sum-of-divisors function m times to n; call n (m,k)-perfect if sigma_m (n) = k*n; sequence gives the (2,10)-perfect numbers.

Original entry on oeis.org

480, 504, 13824, 32256, 32736, 1980342, 1396617984, 3258775296, 14763499520, 38385098752
Offset: 1

Views

Author

N. J. A. Sloane

Keywords

Comments

See also the Cohen-te Riele links under A019276.
No other terms < 5*10^11. - Jud McCranie, Feb 08 2012
a(11) > 4*10^12, if it exists. - Giovanni Resta, Feb 26 2020

Links

Crossrefs

Cf. A019278, A019279, A019281, A019282, A019283, A019284, A019285, A019286, A019288, A019289, A019290, A019291.

Extensions

More terms from Jud McCranie, Nov 13 2001; a(9) Jan 29 2012, a(10) Feb 08 2012

A019288 Let sigma_m (n) be result of applying sum-of-divisors function m times to n; call n (m,k)-perfect if sigma_m (n) = k*n; sequence gives the (2,11)-perfect numbers.

Original entry on oeis.org

4404480, 57669920, 238608384
Offset: 1

Views

Author

N. J. A. Sloane

Keywords

Comments

See also the Cohen-te Riele links under A019276.
No other terms < 5*10^11. - Jud McCranie, Feb 08 2012
a(4) > 4*10^12. - Giovanni Resta, Feb 26 2020
53283599155200, 2914255525994496 and 3887055949004800 are also terms. - Michel Marcus, Feb 27 2020

Links

Crossrefs

Cf. A019278, A019279, A019281, A019282, A019283, A019284, A019285, A019286, A019287, A019289, A019290, A019291.

Programs

  • PARI
    isok(n) = sigma(sigma(n))/n  == 11; \\ Michel Marcus, Feb 27 2020

A019289 Let sigma_m (n) be result of applying sum-of-divisors function m times to n; call n (m,k)-perfect if sigma_m (n) = k*n; sequence gives the (2,12)-perfect numbers.

Original entry on oeis.org

2200380, 8801520, 14913024, 35206080, 140896000, 459818240, 775898880, 2253189120, 16785793024, 22648550400, 36051025920, 51001180160, 144204103680
Offset: 1

Views

Author

N. J. A. Sloane

Keywords

Comments

See also the Cohen-te Riele links under A019276.
No others < 5*10^11. - Jud McCranie, Feb 08 2012
a(14) > 4*10^12. - Giovanni Resta, Feb 26 2020
6640556211576, 82863343951872, 182140970374656, 480965999895576, 590660008673280, 886341160140800, 5562693163417600, 9386507580211200 are also terms. - Michel Marcus, Feb 27 2020

Links

Crossrefs

Cf. A019278, A019279, A019281, A019282, A019283, A019284, A019285, A019286, A019287, A019288, A019290, A019291.

Programs

  • PARI
    isok(n) = sigma(sigma(n))/n  == 12; \\ Michel Marcus, Feb 27 2020

Extensions

More terms from Jud McCranie, Nov 13 2001, a(9) Feb 01 2012, a(10)-a(13) on Feb 08 2012

A019290 Let sigma_m (n) be result of applying sum-of-divisors function m times to n; call n (m,k)-perfect if sigma_m (n) = k*n; sequence gives the (2,13)-perfect numbers.

Original entry on oeis.org

57120, 932064, 3932040, 251650560
Offset: 1

Views

Author

N. J. A. Sloane

Keywords

Comments

See also the Cohen-te Riele links under A019276.
No other terms < 5*10^11. - Jud McCranie, Feb 08 2012
11383810648416 is also a term. See comment in A019278. - Michel Marcus, May 15 2016
a(5) > 4*10^12. - Giovanni Resta, Feb 26 2020
50248050278400, 117245450649600, 86575337046016000 are also terms. - Michel Marcus, Feb 27 2020

Links

Crossrefs

Cf. A019276, A019278, A019279, A019281, A019282, A019283, A019284, A019285, A019286, A019287, A019288, A019289, A019291.

Programs

  • PARI
    isok(n) = sigma(sigma(n))/n == 13; \\ Michel Marcus, May 15 2016

A019291 Let sigma_m (n) be result of applying sum-of-divisors function m times to n; call n (m,k)-perfect if sigma_m (n) = k*n; sequence gives the (2,14)-perfect numbers.

Original entry on oeis.org

217728, 1278720, 2983680, 5621760, 14008320, 298721280, 955367424, 1874780160, 4874428416, 1957928934528
Offset: 1

Views

Author

N. J. A. Sloane

Keywords

Comments

See also the Cohen-te Riele links under A019276.
No other terms < 5*10^11. - Jud McCranie, Feb 08 2012
36095341363200 is also a term. See comment in A019278. - Michel Marcus, May 15 2016
a(11) > 4*10^12. - Giovanni Resta, Feb 26 2020

Links

Crossrefs

Cf. A019276, A019278, A019279, A019281, A019282, A019283, A019284, A019285, A019286, A019287, A019288, A019289, A019290.

Programs

  • PARI
    isok(n) = sigma(sigma(n))/n == 14; \\ Michel Marcus, May 15 2016

Extensions

More terms from Jud McCranie, Nov 13 2001
a(9) from Jud McCranie, Jan 28 2012
a(10) from Giovanni Resta, Feb 26 2020
Showing 1-9 of 9 results.

Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

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