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A257679 The smallest nonzero digit present in the factorial base representation (A007623) of n, 0 if no nonzero digits present. 16
0, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 2, 1, 3, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 2, 1, 2, 1, 1, 1, 2, 1, 3, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 2, 1, 3, 1, 1, 1, 2, 1, 4, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 2, 1, 3, 1, 1, 1, 2, 1, 1 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,5

COMMENTS

a(0) = 0 by convention, because "0" has no nonzero digits present.

a(n) gives the row index of n in array A257503 (equally, the column index for array A257505).

LINKS

Antti Karttunen, Table of n, a(n) for n = 0..5040

FORMULA

If A257687(n) = 0, then a(n) = A099563(n), otherwise a(n) = min(A099563(n), a(A257687(n))).

In other words, if n is either zero or one of the terms of A051683, then a(n) = A099563(n) [the most significant digit of its f.b.r.], otherwise take the minimum of the most significant digit and a(A257687(n)) [value computed by recursing with a smaller value obtained by discarding that most significant digit].

a(0) = 0, and for n >= 1: if A257680(n) = 1, then a(n) = 1, otherwise 1 + a(A257684(n)).

Other identities:

For all n >= 0, a(A001563(n)) = n. [n * n! gives the first position where n appears. Note also that the "digits" (placeholders) in factorial base representation may get arbitrarily large values.]

For all n >= 0, a(2n+1) = 1 [because all odd numbers end with digit 1 in factorial base].

EXAMPLE

Factorial base representation (A007623) of 4 is "20", the smallest digit which is not zero is "2", thus a(4) = 2.

PROG

(Scheme)

(define (A257679 n) (let loop ((n n) (i 2) (mind 0)) (if (zero? n) mind (let ((d (modulo n i))) (loop (/ (- n d) i) (+ 1 i) (cond ((zero? mind) d) ((zero? d) mind) (else (min d mind))))))))

;; Alternative implementations based on given recurrences, using memoizing definec-macro:

(definec (A257679 n) (if (zero? (A257687 n)) (A099563 n) (min (A099563 n) (A257679 (A257687 n)))))

(definec (A257679 n) (cond ((zero? n) n) ((= 1 (A257680 n)) 1) (else (+ 1 (A257679 (A257684 n))))))

(Python)

def A(n, p=2): return n if n<p else A(int(n/p), p+1)*10 + n%p

def a(n): return 0 if n==0 else min([int(i) for i in str(A(n)) if i !='0'])

print [a(n) for n in xrange(201)] # Indranil Ghosh, Jun 19 2017

CROSSREFS

Positions of records: A001563.

Cf. A256450, A257692, A257693 (positions of 1's, 2's and 3's in this sequence).

Cf. A007623, A051683, A099563, A257680, A257684, A257687.

Cf. also A257079, A246359 and arrays A257503, A257505.

Sequence in context: A316439 A086597 A238015 * A031214 A056059 A158819

Adjacent sequences:  A257676 A257677 A257678 * A257680 A257681 A257682

KEYWORD

nonn,base

AUTHOR

Antti Karttunen, May 04 2015

STATUS

approved

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Last modified November 15 22:20 EST 2018. Contains 317252 sequences. (Running on oeis4.)