A282049 Least prime p such that n divides sigma(p*n).

2, 3, 2, 3, 19, 5, 13, 7, 17, 19, 43, 2, 103, 2, 19, 31, 67, 5, 37, 19, 41, 43, 137, 5, 149, 103, 53, 3, 173, 19, 61, 31, 43, 67, 139, 71, 73, 37, 233, 3, 163, 13, 257, 43, 29, 137, 281, 11, 97, 149, 67, 103, 211, 17, 109, 13, 113, 173, 353, 2, 487, 61, 251, 127, 389, 43, 401, 67

Offset: 1

Author

Altug Alkan, Feb 05 2017

Keywords

• nonn

Comments

a(n) <= A038700(n). Numbers n such that a(n) is not equal to A038700(A017666(n)) are 6, 14, 24, 28, 60, 78, 84, 90, 120, 234, 248, 270, 336, 496, 532, 546, ...

Examples

			a(5) = 19 because 5 divides sigma(19*5) = 120 and 19 is the least prime number with this property.
		

Links

• Altug Alkan, Table of n, a(n) for n = 1..30000

Crossrefs

Cf. A000203, A227470

Programs

PARI

a(n) = {my(p=2); while (sigma(p*n) % n != 0, p = nextprime(p+1)); p; } \\ David A. Corneth, Feb 05 2017