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 1-4 of 4 results.

A069792 Triangular numbers in A062918.

Original entry on oeis.org

1, 3, 6, 10, 15, 21, 28, 36, 45, 78, 3741, 4005, 4278, 14028, 224115, 238395, 258121, 994755, 1104841, 2440945, 4601061, 19185915, 26451901, 27073761, 38250631, 611712753, 1787631321, 3620877351, 4427640253, 16786524835, 60302220121, 65003739895, 226236074130, 367188935361, 6710200324191
Offset: 1

Views

Author

Amarnath Murthy, Apr 09 2002

Keywords

Crossrefs

Cf. A062918.

Programs

  • PARI
    rev(n) = eval(concat(Vecrev(Str(n))));
lista(nn) = {s = 0; for (n=1, nn, s += rev(n); if (ispolygonal(s, 3), print1(s, ", ")););} \\ Michel Marcus, Sep 15 2015

Extensions

More terms from Jason Earls, May 16 2002
More terms from Michel Marcus, Sep 15 2015

A262229 Numbers m such that A000217(m) > A062918(m).

Original entry on oeis.org

10, 11, 87, 88, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 895, 896, 897, 898, 899, 900, 901, 902, 903, 904, 905, 906, 907, 908, 909, 910, 911, 912, 913, 914, 915, 916, 917, 918, 919, 920, 921, 922, 923, 924, 925, 926, 927, 928, 929, 930, 931
Offset: 1

Views

Author

Michel Marcus, Sep 15 2015

Keywords

Comments

The sum of the digit reversals of first n natural numbers (A062918) is equal to the sum of the first n natural numbers (A000217) for n=1 to 9. Then 10 is the first time that A000217(m) > A062918(m).

Examples

			For m=10, 1+2+3+4+5+6+7+8+9+10 is > 1+2+3+4+5+6+7+8+9+01, so 10 is a term.

Links

Crossrefs

Cf. A000217, A062918.

Programs

  • Magma
    [m: m in [0..10^3] | m*(m+1)/2 gt &+[Seqint(Reverse(Intseq(i))): i in [0..m]]]; // Bruno Berselli, Sep 16 2015
  • Mathematica
    lim = 931; t = Rest@ Accumulate[Range[0, lim]]; s = Accumulate[Table[FromDigits[Reverse[IntegerDigits@ n]], {n, 1, lim + 1}]];Select[Range@ lim, t[[#]] > s[[#]] &] (* Michael De Vlieger, Sep 15 2015, after Harvey P. Dale at A000217 and Enrique Pérez Herrero at A062918 *)
  • PARI
    isok(n) = n*(n+1)/2 - sum(k=1,n, eval(concat(Vecrev(Str(k))))) > 0;

A074238 Numbers k such that the sum of the reverses of 1,2,...,k is a perfect square.

Original entry on oeis.org

1, 8, 26, 53, 3087, 6173, 8091, 12330, 18358, 42898, 294847, 27382381, 49290155, 426131190, 1350661780, 3161620702, 4461944219, 17625479383, 40766706170, 61554358125, 270930998357
Offset: 1

Views

Author

Joseph L. Pe, Sep 19 2002

Keywords

Comments

a(22) > 5*10^11. - Giovanni Resta, Apr 16 2017

Examples

			reverse(1) + reverse(2) + ... + reverse(25) + reverse(26) = 1 + 2 + ...+ 52 + 62 = 729 = 27^2, so 26 is a term of the sequence.

Crossrefs

Cf. A062918.

Programs

  • Mathematica
    s = 0; r = {}; For[i = 1, i <= 10^5, i++, s = s + FromDigits[Reverse[IntegerDigits[i]]]; If[IntegerQ[s^(1/2)], r = Append[r, i]]]; r

Extensions

a(11)-a(21) from Giovanni Resta, Apr 16 2017

A369612 Numbers k such that k divides Sum_{i=1..k} A004086(i).

Original entry on oeis.org

1, 3, 5, 7, 9, 18, 50, 89, 147, 161, 702, 999, 1323, 1998, 2091, 3042, 3072, 3753, 7982, 13408, 32493, 33867, 99999, 179922, 199998, 368121, 375897, 384876, 741137, 993006, 1173628, 1410462, 2021017, 3160593, 7212528, 9975778, 9999999, 17052657, 18093882, 18782433
Offset: 1

Views

Author

Ctibor O. Zizka, Jan 27 2024

Keywords

Comments

Numbers k that divide A062918(k).

Examples

			Sum_{i=1..18} A004086(i) / 18 = 414/18 = 23 thus k = 18 is a term.

Crossrefs

Cf. A004086, A062918.

Programs

Showing 1-4 of 4 results.

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

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