A396383 - OEIS

A396383

Start with a(1) = 1. Thereafter, a(n) is the least integer not already present in the sequence such that the concatenations of a(n) with a(n-1) and a(n-1) with a(n) have the same number of divisors.

1, 3, 7, 9, 19, 8, 5, 11, 13, 4, 2, 6, 14, 15, 10, 12, 35, 18, 17, 31, 21, 23, 26, 22, 27, 25, 24, 32, 50, 20, 48, 28, 36, 30, 45, 38, 16, 52, 44, 46, 42, 33, 39, 29, 37, 34, 51, 41, 43, 49, 55, 54, 47, 57, 53, 67, 63, 61, 59, 65, 62, 73, 74, 58, 71, 66, 78, 64

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OFFSET

1,2

COMMENTS

Permutation of positive integers?

LINKS

Paolo P. Lava, Table of n, a(n) for n = 1..1000

EXAMPLE

13 and 31 have 2 divisors each: (1, 13) and (1, 31);

198 and 819 have 12 divisors each: (1, 2, 3, 6, 9, 11, 18, 22, 33, 66, 99, 198) and (1, 3, 7, 9, 13, 21, 39, 63, 91, 117, 273, 819)

MAPLE

with(numtheory): P:=proc(q) local a, j, n; a:=[1]; for n from 2 to 100 do