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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A151544 Numbers appearing in the cycles of the "Recurring Digital Invariant Variant" problem described in A151543.

Original entry on oeis.org

1, 2, 3, 4, 5, 6, 7, 8, 9, 136, 153, 160, 217, 244, 259, 352, 370, 371, 407, 496, 586, 664, 736, 853, 862, 1009, 1634, 2178, 2929, 3233, 3283, 4274, 4394, 6514, 6562, 7154, 8208, 9474, 10933, 13154, 18829, 50062, 54748, 58618, 59536, 73318
Offset: 1

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Author

N. J. A. Sloane, May 15 2009 based on email from Eric Angelini, Feb 18 2009

Keywords

Links

Crossrefs

Cf. A151543.

A005188 Armstrong (or pluperfect, or Plus Perfect, or narcissistic) numbers: m-digit positive numbers equal to sum of the m-th powers of their digits.

Original entry on oeis.org

1, 2, 3, 4, 5, 6, 7, 8, 9, 153, 370, 371, 407, 1634, 8208, 9474, 54748, 92727, 93084, 548834, 1741725, 4210818, 9800817, 9926315, 24678050, 24678051, 88593477, 146511208, 472335975, 534494836, 912985153, 4679307774, 32164049650, 32164049651
Offset: 1

Views

Author

N. J. A. Sloane, Robert G. Wilson v

Keywords

Comments

A finite sequence, the 88th and last term being 115132219018763992565095597973971522401.
Let k = d_1 d_2 ... d_n in base 10; then k is in the sequence iff k = Sum_{i=1..n} d_i^n.
These are the fixed points in the "Recurring Digital Invariant Variant" described in A151543.
a(15) = A229381(3) = 8208 is the "Simpsons' narcissistic number".
If a(n) is a multiple of 10, then a(n+1) = a(n) + 1, and if a(n) == 1 (mod 10) then a(n-1) = a(n) - 1 except for n = 1, cf. Examples. - M. F. Hasler, Oct 18 2018
Named after Michael Frederick Armstrong (1941-2020), who used these numbers in his computing class at the University of Rochester in the mid 1960's. - Amiram Eldar, Mar 09 2024

Examples

			153 = 1^3 + 5^3 + 3^3,
8208 = 8^4 + 2^4 + 0^4 + 8^4,
4210818 = 4^7 + 2^7 + 1^7 + 0^7 + 8^7 + 1^7 + 8^7.
The eight terms 370, 24678050, 32164049650, 4338281769391370, 3706907995955475988644380, 19008174136254279995012734740, 186709961001538790100634132976990 and 115132219018763992565095597973971522400 end in a digit zero, therefore their successor a(n) + 1 is the next term a(n+1). This also yields the last term of the sequence. The initial a(1) = 1 is the only term ending in a digit 1 not preceded by a(n) - 1. - _M. F. Hasler_, Oct 18 2018

References

  • Jean-Marie De Koninck, Ces nombres qui nous fascinent, Entry 88, pp. 30-31, Ellipses, Paris 2008.
  • Lionel E. Deimel, Jr. and Michael T. Jones, Finding Pluperfect Digital Invariants: Techniques, Results and Observations, J. Rec. Math., 14 (1981), 87-108.
  • Jean-Pierre Lamoitier, Fifty Basic Exercises. SYBEX Inc., 1981.
  • Clifford A. Pickover, A Passion for Mathematics, Wiley, 2005; see p. 68.
  • Alfred S. Posamentier, Numbers: Their Tales, Types, and Treasures, Prometheus Books, 2015, pp. 242-244.
  • Joe Roberts, The Lure of the Integers, The Mathematical Association of America, 1992, page 36.
  • N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Links

Crossrefs

Cf. A001694, A007532, A005934, A003321, A014576, A046074.
Similar to but different from A023052.
Cf. A151543.
Cf. A010343 to A010354 (bases 4 to 9). - R. J. Mathar, Jun 28 2009

Programs

  • Maple
    filter:= proc(k) local d;
d:= 1 + ilog10(k);
add(s^d, s=convert(k,base,10)) = k
end proc:
select(filter, [$1..10^6]); # Robert Israel, Jan 02 2015
  • Mathematica
    f[n_] := Plus @@ (IntegerDigits[n]^Floor[ Log[10, n] + 1]); Select[ Range[10^7], f[ # ] == # &] (* Robert G. Wilson v, May 04 2005 *)
Select[Range[10^7],#==Total[IntegerDigits[#]^IntegerLength[#]]&] (* Harvey P. Dale, Sep 30 2011 *)
  • PARI
    is(n)=my(v=digits(n));sum(i=1,#v,v[i]^#v)==n \\ Charles R Greathouse IV, Nov 20 2012
  • PARI
    select( is_A005188(n)={n==vecsum([d^#n|d<-n=digits(n)])}, [0..9999]) \\ M. F. Hasler, Nov 18 2019
  • Python
    from itertools import combinations_with_replacement
A005188_list = []
for k in range(1,10):
    a = [i**k for i in range(10)]
    for b in combinations_with_replacement(range(10),k):
        x = sum(map(lambda y:a[y],b))
        if x > 0 and tuple(int(d) for d in sorted(str(x))) == b:
            A005188_list.append(x)
A005188_list = sorted(A005188_list) # Chai Wah Wu, Aug 25 2015

Extensions

32164049651 from Amit Munje (amit.munje(AT)gmail.com), Oct 07 2006
In order to agree with the Definition, first comment modified by Jonathan Sondow, Jan 02 2015
Comment in name moved to comment section and links edited by M. F. Hasler, Oct 18 2018
"Positive" added to definition by N. J. A. Sloane, Nov 18 2019

A157714 Base-10 pseudo-altruistic numbers.

Original entry on oeis.org

136, 160, 217, 244, 259, 352, 496, 586, 664, 736, 853, 862, 1009, 2178, 2929, 3233, 3283, 4274, 4394, 6514, 6562, 7154, 10933, 13154, 18829, 50062, 58618, 59536, 73318, 76438, 124618, 282595, 312962, 329340, 376761, 537059, 578955, 681069
Offset: 1

Views

Author

Hans Havermann, Mar 04 2009

Keywords

Comments

These integers reoccur (with a period greater than 1) upon the iteration of raising every digit to the power of the number's length and summing.
If the reoccurrence is immediate (period 1), the numbers are (instead) narcissistic (A005188).

Examples

			2929 is pseudo-altruistic because 2929 -> 13154 (2^4 + 9^4 + 2^4 + 9^4) -> 4394 (1^5 + 3^5 + 1^5 + 5^5 + 4^5) -> 7154 (4^4 + 3^4 + 9^4 + 4^4) -> 3283 (7^4 + 1^4 + 5^4 + 4^4) -> 4274 (3^4 + 2^4 + 8^4 + 3^4) -> 2929 (4^4 + 2^4 + 7^4 + 4^4).

Links

Crossrefs

Cf. A005188. The "Recurring Digital Invariant Variant" is described in more detail in A151543.
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Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

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