A159588 - OEIS

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A159588

a(n) is the smallest number not yet in the sequence with the same number of prime factors as n (with repetition), but relatively prime to n.

1, 3, 2, 9, 7, 25, 5, 27, 4, 21, 13, 125, 11, 15, 14, 81, 19, 175, 17, 63, 10, 35, 29, 625, 6, 33, 8, 45, 23, 343, 37, 243, 26, 39, 22, 875, 31, 49, 34, 189, 43, 275, 41, 75, 28, 51, 53, 3125, 38, 99, 46, 105, 47, 1225, 57, 135, 55, 65, 61, 2401, 59, 69, 20, 729, 58, 245, 71

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,2

COMMENTS

This is a self-inverse permutation of the positive integers.

LINKS

Rémy Sigrist, Table of n, a(n) for n = 1..5000

Rémy Sigrist, Scatterplot of (n, a(n)) for n, a(n) <= 25000

PROG

(PARI) invect(v, n, x)=for(i=1, n, if(v[i]==x, return(1))); 0

nextnew(v, n)=local(k); k=1; while(!R(n, k)||invect(v, n-1, k), k++); k

newvect(n)=local(v); v=vector(n); for(k=1, n, v[k]=nextnew(v, k)); v