A306661 Numbers with chained divisors: Numbers k with divisors such that the last digit of every divisor is the same as the first digit of the next divisor.

1, 11, 13, 17, 19, 101, 103, 107, 109, 113, 121, 127, 131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 181, 191, 193, 197, 199, 1009, 1013, 1019, 1021, 1031, 1033, 1039, 1049, 1051, 1061, 1063, 1069, 1087, 1091, 1093, 1097, 1103, 1109, 1111

Offset

1,2

Comments

All prime numbers whose first digit is 1 (A045707) have this property.

The first composite numbers having this property are A307858: 121, 1111, 1207, ...

Links

Table of n, a(n) for n=1..46.

Example

14641 is such a number because its divisors are 1, 11, 121, 1331, 14641.
Also, 90043 is in the sequence because its divisors are 1, 127, 709, 90043 and the last digit of every divisor is the first digit of the next one.

Mathematica

Select[Range@1500, And@@(Last@#[[1]]==First@#[[2]]&/@Partition[IntegerDigits/@Divisors@#, 2, 1])&]

Crossrefs

A307858 and A045707 are subsequences.

Sequence in context: A087201 A068492 A206287 * A045707 A032591 A088265

Adjacent sequences: A306658 A306659 A306660 * A306662 A306663 A306664

Keyword

nonn,base

Author

Giorgos Kalogeropoulos, May 05 2019

Status

approved