OFFSET
1,3
COMMENTS
Also row n lists the divisors of n and the primes < n that do not divide n, in increasing order.
Also row n lists the nonprime divisors of n and the primes <= n, in increasing order.
The motivation for this sequence is A046022 which is also the union of the odd primes and the divisors of 4. Here the n-th row of triangle can be interpreted as the initial terms of the infinite sequence defined as the union of the prime numbers and the divisors of n.
EXAMPLE
For n = 10, the divisors of 10 are 1, 2, 5, 10. The primes less than 10 that do not divide 10 are 3 and 7. So row 10 is 1, 2, 3, 5, 7, 10.
On the other hand, the primes <= n are 2, 3, 5, 7. The nonprime divisors of n are 1, 10. So row 10 is 1, 2, 3, 5, 7, 10.
Written as an irregular triangle the sequence begins:
1;
1, 2;
1, 2, 3;
1, 2, 3, 4;
1, 2, 3, 5;
1, 2, 3, 5, 6;
1, 2, 3, 5, 7;
1, 2, 3, 4, 5, 7, 8;
1, 2, 3, 5, 7, 9;
1, 2, 3, 5, 7, 10;
1, 2, 3, 5, 7, 11;
1, 2, 3, 4, 5, 6, 7, 11, 12;
1, 2, 3, 5, 7, 11, 13;
1, 2, 3, 5, 7, 11, 13, 14;
1, 2, 3, 5, 7, 11, 13, 15;
1, 2, 3, 4, 5, 7, 8, 11, 13, 16;
1, 2, 3, 5, 7, 11, 13, 17;
1, 2, 3, 5, 6, 7, 9, 11, 13, 17, 18;
1, 2, 3, 5, 7, 11, 13, 17, 19;
1, 2, 3, 4, 5, 7, 10, 11, 13, 17, 19, 20;
1, 2, 3, 5, 7, 11, 13, 17, 19, 21;
1, 2, 3, 5, 7, 11, 13, 17, 19, 22;
1, 2, 3, 5, 7, 11, 13, 17, 19, 23;
1, 2, 3, 4, 5, 6, 7, 8, 11, 12, 13, 17, 19, 23, 24;
CROSSREFS
KEYWORD
nonn,tabf,less
AUTHOR
Omar E. Pol, Nov 04 2013
STATUS
approved