A039914 Smallest k>1 such that k(p-1)-1 is divisible by p^2, p=n-th prime.

5, 5, 19, 41, 109, 155, 271, 341, 505, 811, 929, 1331, 1639, 1805, 2161, 2755, 3421, 3659, 4421, 4969, 5255, 6161, 6805, 7831, 9311, 10099, 10505, 11341, 11771, 12655, 16001, 17029, 18631, 19181, 22051, 22649, 24491, 26405, 27721, 29755, 31861

Offset: 1

Author

Felice Russo

Keywords

• nonn

Examples

			a(1)=5 because 5(2-1)-1=4 is divisible by 2^2.
		

Crossrefs

Cf. A039678.

A306190 is an essentially identical sequence.

Programs

PARI

a(n) = {my(p = prime(n), k = 2); while ((k*(p-1)-1) % p^2, k++); k;} \\ Michel Marcus, Sep 28 2013

Extensions

Added constraint on k to the definition, otherwise a(1)=1 - R. J. Mathar, Oct 10 2010