A286607 -id:A286607 - cp's OEIS frontend

A118363 Factorial base Niven (or Harshad) numbers: numbers that are divisible by the sum of their factorial base digits.

1, 2, 4, 6, 8, 9, 12, 16, 18, 20, 24, 26, 27, 30, 35, 36, 40, 48, 52, 54, 56, 60, 70, 72, 75, 80, 90, 91, 96, 105, 108, 112, 117, 120, 122, 123, 126, 132, 135, 140, 144, 148, 150, 152, 156, 161, 168, 175, 180, 186, 192, 204, 208, 210, 222, 224, 240, 244, 245, 246

Offset: 1

Alonso del Arte, May 15 2006

Also called "Fiven" numbers [Dahlenberg and Edgar]. - N. J. A. Sloane, Jun 25 2018

			a(8) = 16 because it is written 220 in factorial base and 2 + 2 + 0 = 4, which is a divisor of 16.
17 is not on the list because it is written 221 in factorial base and 2 + 2 + 1 = 5, which is not a divisor of 17.

Antti Karttunen, Table of n, a(n) for n = 1..10000
Paul Dahlenberg and Tom Edgar, Consecutive factorial base Niven numbers, The Fibonacci Quarterly, Vol. 56, No. 2 (2018), pp. 163-166.
Index entries for sequences related to factorial base representation.

Cf. A007623 (integers written in factorial base), A005349 (base 10 Harshad numbers).
Cf. A286607 (complement), A034968, A286590.
Positions of zeros in A286604.

(*For the definition of the factorial base version of IntegerDigits, see A007623*) Select[Range[250],IntegerQ[ #/(Plus@@factBaseIntDs[ # ])]&]

is(n) = {my(k = n, m = 2, r, s = 0); while([k, r] = divrem(k, m); k != 0 || r != 0, s += r; m++); !(n % s);} \\ Amiram Eldar, Oct 08 2024

def a007623(n, p=2): return n if nIndranil Ghosh, Jun 21 2017

A286604 a(n) = n mod sum of digits of n in factorial base.

Original entry on oeis.org

0, 0, 1, 0, 2, 0, 1, 0, 0, 1, 3, 0, 1, 2, 3, 0, 2, 0, 3, 0, 1, 2, 5, 0, 1, 0, 0, 1, 1, 0, 1, 2, 1, 2, 0, 0, 1, 2, 4, 0, 5, 2, 3, 4, 3, 4, 5, 0, 1, 2, 3, 0, 3, 0, 3, 0, 2, 3, 5, 0, 1, 2, 3, 4, 2, 1, 1, 2, 6, 0, 7, 0, 1, 2, 0, 1, 5, 2, 4, 0, 3, 4, 6, 4, 1, 2, 3, 4, 1, 0, 0, 1, 5, 6, 5, 0, 2, 3, 3, 4, 3, 2, 1, 2, 0, 1, 3, 0, 4, 5, 7, 0, 5, 2, 3, 4, 0, 1, 9, 0

Offset: 1

Antti Karttunen, Jun 18 2017

Antti Karttunen, Table of n, a(n) for n = 1..10080
Index entries for sequences related to factorial base representation.

Cf. A034968, A286606.

Cf. A118363 (positions of zeros), A286607 (of nonzeros).

a[n_] := Module[{k = n, m = 2, r, s = 0}, While[{k, r} = QuotientRemainder[k, m]; k != 0|| r != 0, s += r; m++]; Mod[n, s]]; Array[a, 100] (* Amiram Eldar, Feb 21 2024 *)

def a007623(n, p=2): return n if nIndranil Ghosh, Jun 21 2017

(define (A286604 n) (modulo n (A034968 n)))

a(n) = n mod A034968(n).

A377384 a(n) is the number of iterations that n requires to reach a noninteger or a factorial number under the map x -> x / f(x), where f(k) = A034968(k) is the sum of digits in the factorial-base representation of k; a(n) = 0 if n is a factorial number.

Original entry on oeis.org

0, 0, 1, 1, 1, 0, 1, 2, 2, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 0, 1, 2, 3, 1, 1, 2, 1, 1, 1, 1, 2, 2, 1, 1, 1, 3, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 2, 1, 2, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 2, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1

Offset: 1

Amiram Eldar, Oct 27 2024

The factorial numbers are fixed points of the map, since f(k!) = 1 for all k >= 0. Therefore they are arbitrarily assigned the value a(k!) = 0.

Each number n starts a chain of a(n) integers: n, n/f(n), (n/f(n))/f(n/f(n)), ..., of them the first a(n)-1 integers are factorial-base Niven numbers (A118363).

			a(8) = 2 since 8/f(8) = 4 and 4/f(4) = 2 is a factorial number that is reached after 2 iterations.
a(27) = 3 since 27/f(27) = 9, 9/f(9) = 3 and 3/f(3) = 3/2 is a noninteger that is reached after 3 iterations.

Amiram Eldar, Table of n, a(n) for n = 1..10000

Cf. A000005, A000142, A034968, A118363, A286607, A377385, A377386.

Analogous sequences: A376615 (binary), A377208 (Zeckendorf).

fdigsum[n_] := Module[{k = n, m = 2, r, s = 0}, While[{k, r} = QuotientRemainder[k, m]; k != 0 || r != 0, s += r; m++]; s]; a[n_] := a[n] = Module[{s = fdigsum[n]}, If[s == 1, 0, If[!Divisible[n, s], 1, 1 + a[n/s]]]]; Array[a, 100]

fdigsum(n) = {my(k = n, m = 2, r, s = 0); while([k, r] = divrem(k, m); k != 0 || r != 0, s += r; m++); s;}
a(n) = {my(f = fdigsum(n)); if(f == 1, 0, if(n % f, 1, 1 + a(n/f)));}

def f(n, p=2): return n if nMichael S. Branicky, Oct 27 2024

a(n) = 0 if and only if n is in A000142 (by definition).
a(n) = 1 if and only if n is in A286607.
a(n) >= 2 if and only if n is in A118363 \ A000142 (i.e., n is a factorial-base Niven number that is not a factorial number).
a(n) >= 3 if and only if n is in A377385 \ A000142.
a(n) >= 4 if and only if n is in A377386 \ A000142.
a(n) < A000005(n).

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A118363 Factorial base Niven (or Harshad) numbers: numbers that are divisible by the sum of their factorial base digits.

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A286604 a(n) = n mod sum of digits of n in factorial base.

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A377384 a(n) is the number of iterations that n requires to reach a noninteger or a factorial number under the map x -> x / f(x), where f(k) = A034968(k) is the sum of digits in the factorial-base representation of k; a(n) = 0 if n is a factorial number.

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