A320026 Odd squarefree numbers k for which m >= 0 can be found such that k*2^m divides sigma(k*2^m).

1, 3, 7, 15, 21, 31, 127, 1023, 8191, 131071, 180213, 524287, 1796165, 3112865, 5388495, 9338595, 2147483647, 2305843009213693951, 618970019642690137449562111, 162259276829213363391578010288127, 170141183460469231731687303715884105727

Offset

1,2

Comments

The Mersenne primes A000668 are a subsequence.

Links

Table of n, a(n) for n=1..21.

Example

1023 is in this sequence because 1023 = 3*11*31 and 1023*2^9 divides 1571328 which is the sum of divisors of 1023*2^9.

Crossrefs

Cf. A000203, A000668, A007691, A056911, A320024.

Sequence in context: A373941 A139208 A324727 * A146435 A046932 A015821

Adjacent sequences: A320023 A320024 A320025 * A320027 A320028 A320029

Keyword

nonn

Author

Peter Luschny, Oct 13 2018

Status

approved