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.

A135207 a(n)=Sum_digits{n^Sum_digits[a(n-1)]}, with a(0)=1.

Original entry on oeis.org

1, 1, 2, 9, 19, 40, 18, 28, 37, 45, 1, 2, 9, 46, 67, 81, 64, 55, 54, 73, 7, 36, 55, 49, 99, 109, 64, 63, 64, 34, 18, 55, 76, 81, 73, 73, 72, 82, 79, 90, 19, 49, 99, 136, 82, 63, 64, 70, 54, 73, 40, 27, 82, 82, 72, 82, 70, 72, 91, 49, 36, 64, 91, 99, 145, 79, 126, 82, 58, 126, 28
Offset: 0

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Author

Keywords

Crossrefs

Programs

  • Maple
    P:=proc(n) local a,i,k,w; a:=1; print(a); for i from 1 by 1 to n do w:=0; k:=a; while k>0 do w:=w+k-(trunc(k/10)*10); k:=trunc(k/10); od; k:=i^w; w:=0; while k>0 do w:=w+k-(trunc(k/10)*10); k:=trunc(k/10); od; a:=w; print(w); od; end: P(100);
  • Mathematica
    nxt[{n_,a_}]:={n+1,Total[IntegerDigits[(n+1)^Total[IntegerDigits[a]]]]}; NestList[nxt,{0,1},70][[;;,2]] (* Harvey P. Dale, Nov 03 2024 *)

A138572 Numbers k that divide the sum of the digits of k^k in base 2.

Original entry on oeis.org

1, 6, 122, 2126, 7910, 8254, 16201, 32312, 32426, 32998, 65436, 261649, 261803, 1044017, 1050183, 4194999
Offset: 1

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Author

Robert Gerbicz, May 12 2008

Keywords

Comments

Conjecture: the sequence is infinite.
The quotients are 1, 1, 3, 5, 6, 6, 7, 6, 7, 7, 7, 9, 9, 10, 10, 11.
From Nick Hobson, Feb 05 2024: (Start)
a(17) > 4500000.
Observation: the known terms of this sequence are near a power of 2:
k log_2(k)
1 0.000000
6 2.584963
122 6.930737
2126 11.053926
7910 12.949462
8254 13.010878
16201 13.983795
32312 14.979782
32426 14.984863
32998 15.010091
65436 15.997797
261649 17.997273
261803 17.998122
1044017 19.993714
1050183 20.002209
4194999 22.000239
Searching near 2^23, 2^24, and 2^25 finds term 16783381.
(End)

Examples

			6^6 = 1011011001000000_2; 1+0+1+1+0+1+1+0+0+1+0+0+0+0+0+0 = 6; 6 mod 6 = 0.
		

Crossrefs

Cf. A108827.

Programs

  • C
    See Links section.
  • Mathematica
    Select[Range[1100000],Divisible[Total[IntegerDigits[#^#,2]],#]&] (* Harvey P. Dale, Dec 18 2014 *)
  • PARI
    isok(k) = !(hammingweight(k^k) % k); \\ Michel Marcus, Aug 20 2021
    

Extensions

a(12)-a(15) from Lars Blomberg, Jul 01 2011
a(16) from Nick Hobson, Feb 05 2024

A140604 Least nontrivial number k such that the sum of the digits of k^k (mod k) == n.

Original entry on oeis.org

1, 4, 55, 6, 7, 8, 12, 2236, 11, 15, 14, 20, 21, 17, 274, 35, 22, 44, 36, 82, 73, 41, 29, 28, 26, 115, 85, 98, 2054, 31, 46, 502, 40, 39, 79, 3248, 45, 38, 128, 64, 511, 80, 183, 83, 76, 47, 127, 176, 52, 70, 190, 57, 65, 425, 63, 56, 95, 59, 10327, 794, 1248, 89, 410, 69
Offset: 0

Views

Author

Robert G. Wilson v, May 17 2008

Keywords

Examples

			1^1 (mod 1)==0; 4^4=256 so 13 (mod 4)==1; 55^55=... so 442 (mod 55)==2, 6^6=46656 so 27 (mod 6)==3; etc.
		

Crossrefs

Programs

  • Mathematica
    t = Table[0, {101}]; Do[ a = Mod[Plus @@ IntegerDigits[n^n], n]; If[a < 101 && t[[a + 1]] == 0, t[[a + 1]] = n; Print[{a, n}]], {n, 10000}]
Showing 1-3 of 3 results.