A359650 Smallest prime factor q of (2^(p-1)-1) / (3*p) with prime p such that q is greater than p (increasing p, cf. A359387).

31, 89, 178481, 233, 13367, 6361, 499, 62020897, 3391, 1049, 4153, 1433, 7068569257, 1327, 1399, 1913, 54217, 80929, 26371, 7753, 855857, 5867, 3449, 48731, 7707719, 12619129, 104369, 32051, 78557207, 67219, 1676083, 34513, 22291, 4567, 14563, 830833, 2731, 343081

Offset: 1

Author

Alain Rocchelli, Jan 09 2023

Keywords

• nonn

Examples

			For p=7,  (2^6-1)/(3*7) = 3 and 3 is not greater than 7.
For p=11, (2^10-1)/(3*11) = 31, which is greater than 11, so a(1)=31.
For p=13, (2^12-1)/(3*13) = 105 = 3*5*7 and 3 is not greater than 13.
For p=17, (2^16-1)/(3*17) = 1285 = 5*257 and 5 is not greater than 17.
For p=19, (2^18-1)/(3*19) = 4599 = 3^2*7*73 and 3 is not greater than 19.
For p=23, (2^22-1)/(3*23) = 60787 = 89*683 and 89 is greater than 23, so a(2)=89.
		

Crossrefs

Cf. A000720, A020639, A096060, A359387.

Formula

a(n) = A020639(A096060(A000720(A359387(n)))). - Michel Marcus, Jan 14 2023