A256464 a(n) is the index, in the A256440 triangle, of the first row where n is the n-th term of the row.

1, 2, 5, 4, 13, 6, 23, 9, 19, 13, 43, 12, 59, 22, 27, 19, 79, 19, 97, 22, 41, 35, 113, 24, 89, 43, 59, 33, 157, 31, 173, 41, 77, 61, 101, 36, 211, 71, 95, 45, 239, 46, 257, 59, 71, 86, 281, 48, 209, 73, 127, 73, 331, 62, 167, 67, 143, 111, 373, 60, 389, 121

Offset: 1

Author

Michel Marcus, Mar 30 2015

Keywords

• nonn

Comments

The integers for which a(n)=n are 1, 2, 4, 6, 12, 24, 36, 48, 60, ... : A004394.

The integers for which a(n)=n-1 are 3, 8, 18, 30, 72, ...: A247022 (except 3).

Examples

			Triangle A256440 starts:
1;
1, 2;
1, 3, 2;
1, 3, 2, 4;
1, 5, 3, 2, 4;
1, 5, 3, 2, 4, 6;
1, 7, 5, 3, 2, 4, 6;
...
a(1)=1 because row 1 is the first row where 1 is the 1st term of the row.
a(2)=2 because row 2 is the first row where 2 is the 2nd term of the row.
a(3)=5 because row 5 is the first row where 3 is the 3rd term of the row.
		

Crossrefs

Cf. A004394, A247022, A256440.

Programs

PARI

posf(n) = {i = n; stop = 0; while (! stop, v = vector(i, k, sigma(k)/k); w = vecsort(v, , 1); pos = posv(n, w); if (pos == n, stop=1, i++);); i;}