A276654 a(n) = the smallest number k>1 such that floor(Sum_{p|k} 0.p) = n where p runs through the prime divisors of k.

2, 21, 2905, 281785, 47740490, 9178864590, 8533159052845, 1817562878255985, 1801204812351681135, 787408225243814333670

Offset

0,1

Comments

Here 0.p means the decimal fraction obtained by writing p after the decimal point, e.g. 0.11 = 11/100.

The first few values of Sum_{p|n} 0.p are: 1/5, 3/10, 1/5, 1/2, 1/2, 7/10, 1/5, 3/10, 7/10, ...

Subsequence of A005117. - Chai Wah Wu, Sep 15 2016

Links

Table of n, a(n) for n=0..9.

Example

Number 2905 is the smallest number k with floor(Sum_{p|k} 0.p) = 2; set of prime divisors of 2905: {5, 7, 83}; floor(Sum_{p|2905} 0.p) = 0.5 + 0.7 + 0.83 = floor(2.03) = 2.

Mathematica

Table[k = 2; While[f = FactorInteger[k][[All, 1]];
  Floor[Total[f*10^-IntegerLength[f]]] != n, k++];
k, {n, 0, 3}] (* Robert Price, Sep 20 2019 *)

Prog

(Magma) A276654:=func<n|exists(r){k:k in[2..1000000] | Floor(&+[d / (10^(#Intseq(d))): d in PrimeDivisors(k)]) eq n}select r else 0>; [A276654(n): n in[0..3]]

Crossrefs

Cf. A005117, A276513, A276651, A276652, A276653, A276655.

Sequence in context: A022470 A080815 A351580 * A114846 A195165 A201973

Adjacent sequences: A276651 A276652 A276653 * A276655 A276656 A276657

Keyword

nonn,base,more

Author

Jaroslav Krizek, Sep 11 2016

Extensions

a(4) from Michel Marcus, Sep 11 2016

a(5)-a(9) from Giovanni Resta, Aug 31 2019

Status

approved