A131931 -id:A131931 - cp's OEIS frontend

A131929 Number of prime factors of n that are contained in decimal representation of n.

0, 1, 1, 0, 1, 0, 1, 0, 0, 0, 1, 1, 1, 0, 1, 0, 1, 0, 1, 1, 0, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 0, 1, 0, 1, 1, 1, 0, 1, 0, 1, 0, 0, 1, 0, 1, 1, 0, 1, 0, 0, 0, 1, 0, 1, 1, 1, 0, 1, 0, 1, 0, 0, 1, 1, 1, 1, 0, 1, 0, 1, 0, 1, 0, 0, 1, 1, 0, 1, 0, 0, 0, 1, 0, 0, 1, 1, 0, 1, 0, 1, 0, 0, 0, 1, 1, 1, 0, 1

Offset: 1

Reinhard Zumkeller, Jul 30 2007

a(A050695(n)) = 0; a(A131930(n)) > 0;

a(A131931(n)) = n and a(m) <> n for m < A131931(n).

			a(230) = a(23*5*2) = #{2,23} = 2.

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Cf. A131930, A131931.

A318965 a(n) is the smallest number containing all its n prime factors in its decimal representation.

Original entry on oeis.org

2, 135, 735, 21372, 271362, 4773132, 113678565, 11317129824, 131175822960, 7113719552940, 255360234137190, 12411792985131540

Offset: 1

Giovanni Resta, Sep 06 2018

			a(2) = 135 = 3^3 * 5,
a(3) = 735 = 3 * 5 * 7^2,
a(4) = 21372 = 2^2 * 3 * 13 * 137,
a(5) = 271362 = 2 * 3 * 7^2 * 13 * 71,
a(6) = 4773132 = 2^2 * 3^2 * 7 * 13 * 31 * 47.
a(7) = 113678565 = 3 * 5 * 7 * 11 * 13 * 67 * 113.

Cf. A131929, A131930, A131931, A239060, A115738.

a[n_] := Block[{k=1, s, f}, While[True, k++; If[Length[f = FactorInteger[k]] == n, s = ToString@k; If[AllTrue[First /@ f, StringPosition[s, ToString@ #] != {} &], Break[]]]]; k]; Array[a, 5]

cp's OEIS Frontend

A131929 Number of prime factors of n that are contained in decimal representation of n.

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