A275380 Number of odd prime factors (with multiplicity) of generalized Fermat number 7^(2^n) + 1.

0, 2, 1, 2, 2, 3, 3, 5, 3, 6

Offset: 0

Author

Arkadiusz Wesolowski, Jul 25 2016

Keywords

• nonn
• hard
• more

Examples

			b(n) = (7^(2^n) + 1)/2.
Complete Factorizations
b(0) = 2*2
b(1) = 5*5
b(2) = 1201
b(3) = 17*169553
b(4) = 353*47072139617
b(5) = 7699649*134818753*531968664833
b(6) = 35969*1110623386241*15266848196793556098085000332888634369
b(7) = 257*769*197231873*6856531741041792239054980342217258517995521*P52
b(8) = 28667393*126575155274810369*P192
b(9) = 13313*943558259713*
       275102002206713516320479233*1338330888777063359811677099009*
       656929861401793262700329631944023570433*P321
		

Crossrefs

Cf. A078304, A273948.

Formula

a(n) = A001222(A078304(n)) for n > 0. - Felix Fröhlich, Jul 25 2016

Extensions

a(9) was found by Nestor de Araújo Melo and Geoffrey Reynolds (2008)