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 1-3 of 3 results.

A114927 Numbers n such that sigma(n)=3*reversal(n).

Original entry on oeis.org

41, 291552, 692133, 2946762, 8231796, 21732508611, 27892659612
Offset: 1

Views

Author

Farideh Firoozbakht, Jan 28 2006

Keywords

Comments

No more terms through 10^9. - Ryan Propper, Jan 08 2007
a(8) > 10^12. - Giovanni Resta, Oct 28 2012

Crossrefs

Cf. A069216, A105324, A114928.

Programs

  • Mathematica
    Do[If[DivisorSigma[1, n] == 3*FromDigits[Reverse[IntegerDigits[n]]], Print[n]], {n, 20000000}]

Extensions

a(6)-a(7) from Donovan Johnson, Dec 21 2008

A115748 Numbers n such that sigma(n)=7*reversal(n).

Original entry on oeis.org

63301, 651001, 6967932, 2158803990, 88858402692
Offset: 1

Views

Author

Farideh Firoozbakht, Feb 12 2006

Keywords

Comments

a(6) > 10^12. - Giovanni Resta, Oct 28 2012

Examples

			2158803990 is in the sequence because sigma(2158803990)
=6951619584=7*993088512=7*reversal(2158803990).

Crossrefs

Cf. A069216, A105324, A114928.

Extensions

a(5) from Donovan Johnson, Dec 21 2008

A115749 Numbers n such that sigma(n)=8*reversal(n).

Original entry on oeis.org

861, 951, 2070, 8241, 900051, 8864151, 9000051, 82000041, 8200000041, 82000000041
Offset: 1

Views

Author

Farideh Firoozbakht, Feb 12 2006

Keywords

Comments

If p=3*10^n+17 is prime then 3*p is in the sequence because sigma(3*p)=4*(3*10^n+18)=12*10^n+72=8*(15*10^(n-1)+9)=8* reversal(9*10^n+51)=8*reversal(3*p). Also if p=(2*10^n+1)/3 is prime then 123*p is in the sequence (the proof is easy). Next term is greater than 13*10^7.
a(11) > 10^12. - Giovanni Resta, Oct 28 2012

Examples

			82000041 is in the sequence because sigma(82000041)
=112000224=8*14000028=8*reversal(82000041).

Crossrefs

Cf. A069216, A105324, A114928, A115747, A115748.

Programs

  • Mathematica
    Do[If[DivisorSigma[1,n]==8*FromDigits[Reverse[IntegerDigits[n]]],Print[n]],{n,130000000}]

Extensions

a(9)-a(10) from Donovan Johnson, Dec 21 2008
Showing 1-3 of 3 results.

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

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