A358415 a(n) is the prime or perfect or amicable or sociable number encountered in the aliquot sequence for 2^n.
2, 3, 7, 3, 31, 41, 127, 41, 43, 7, 113, 7, 8191, 6, 6, 313, 131071, 211457, 524287, 53, 4217, 433, 41, 547, 2243, 691921, 21275809, 673, 76831, 467, 2147483647, 89, 112337, 401, 17681, 9342799, 12011, 9511, 19, 1061129, 164524721, 5460123943, 71, 106661, 33188053169, 211, 41
Offset: 1
Keywords
Links
- Michel Marcus, Table of n, a(n) for n = 1..200
- Jean-Luc Garambois, Aliquot sequences starting on integer powers 2^i
Programs
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PARI
a(n) = my(b=2); if (n==1, return(b)); my(list = List(), s=b^n); for (i=1, oo, s = sigma(s) - s; if (#select(x->(x==s), list), return(s)); if (isprime(s), return (s)); listput(list, s););
Formula
a(n) = A115350(2^n).