A366896 a(n) is the least positive integer not already in the sequence with the property that the concatenation a(0)a(1)...a(n) forms an integer with n distinct prime factors.

1, 3, 4, 2, 11, 21, 30, 216, 118, 170, 1092, 8484, 97104, 96720, 493170, 251496, 1380652, 12137510, 113661933

Offset

0,2

Links

Table of n, a(n) for n=0..18.

Example

a(0) = 1 and 1 has 0 distinct prime factors.
a(1) = 3 and 13 has 1 distinct prime factor.
a(2) = 4 and 134 = 2*67 has 2 distinct prime factors.
a(3) = 2 and 1342 = 2*11*61 has 3 distinct prime factors.
a(4) = 11 and 134211 = 3*7^2*11*83 has 4 distinct prime factors.

Mathematica

a[0]=1; a[n_]:=a[n]=Block[{t=1}, While[PrimeNu[FromDigits@Flatten[IntegerDigits/@Join[Array[a, n, 0], {t}]]]!=n||MemberQ[Array[a, n, 0], t], t++]; t]; Array[a, 11, 0]

Crossrefs

Cf. A001221.

Sequence in context: A352417 A286681 A019474 * A072565 A159672 A059114

Adjacent sequences: A366893 A366894 A366895 * A366897 A366898 A366899

Keyword

nonn,base,more,changed

Author

Giorgos Kalogeropoulos, Oct 26 2023

Extensions

a(13) from Michael S. Branicky, Oct 27 2023

a(14) from Sean A. Irvine, Dec 03 2023

a(15)-a(17) from Daniel Suteu, Dec 03 2023

a(18) from Daniel Suteu, Aug 11 2024

Status

approved