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

1,1

Links

Michel Marcus, Table of n, a(n) for n = 1..200

Jean-Luc Garambois, Aliquot sequences starting on integer powers 2^i

Formula

a(n) = A115350(2^n).

Prog

(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); );

Crossrefs

Cf. A001065, A115350, A358239, A358266.

Sequence in context: A085641 A086516 A281962 * A245675 A245617 A109205

Adjacent sequences: A358412 A358413 A358414 * A358416 A358417 A358418

Keyword

nonn

Author

Michel Marcus, Nov 14 2022

Status

approved