a(n) = prime that is eventually reached when x -> sigma(x)-1 is repeatedly applied to 2^n-1, or -1 if no prime is ever reached.

A291776

a(n) = prime that is eventually reached when x -> sigma(x)-1 is repeatedly applied to 2^n-1, or -1 if no prime is ever reached.

Terms

    a(0) =3a(1) =7a(2) =23a(3) =31a(4) =103a(5) =127a(6) =431a(7) =911a(8) =1847a(9) =6719a(10) =10487a(11) =8191a(12) =56999a(13) =41399a(14) =135647a(15) =131071a(16) =560159a(17) =524287a(18) =1999871a(19) =3982271a(20) =5909759a(21) =17512991a(22) =46092239a(23) =46335599a(24) =164460119a(25) =186592247a(26) =736727807a(27) =3926707199a(28) =4146049487a(29) =2147483647

External references