A080944 -id:A080944 - cp's OEIS frontend

A080943 Numbers having exactly two divisors that are also suffixes in binary representation.

3, 5, 6, 7, 9, 10, 11, 12, 13, 14, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 28, 29, 31, 33, 34, 35, 36, 37, 38, 40, 41, 42, 43, 44, 46, 47, 48, 49, 50, 52, 53, 55, 56, 57, 58, 59, 61, 62, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 76, 77, 79, 80, 81, 82, 83, 84, 86, 88, 89, 91, 92

Offset: 1

Reinhard Zumkeller, Feb 25 2003

A080942(a(n))=2, the two divisors are n and 1 for odd numbers and 2 for even numbers.

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Cf. A080945, A080944, A007088, A080940, A080941.

a080943 n = a080943_list !! (n-1)
a080943_list = filter ((== 2) . a080942) [1..]
-- Reinhard Zumkeller, Mar 27 2014

from itertools import count, islice
from sympy import divisors
def A080943_gen(startvalue=3): # generator of terms >= startvalue
    return filter(lambda n:(m:=n&-n)!=n and all(d==m or d==n or (d^n)&((1<A080943_list = list(islice(A080943_gen(),20)) # Chai Wah Wu, Jun 20 2023

A080945 Numbers having more than two divisors that are also suffixes in binary representation.

Original entry on oeis.org

15, 27, 30, 39, 45, 51, 54, 60, 63, 75, 78, 85, 87, 90, 99, 102, 108, 111, 119, 120, 123, 125, 126, 135, 147, 150, 153, 156, 159, 165, 170, 171, 174, 175, 180, 183, 187, 195, 198, 204, 205, 207, 216, 219, 221, 222, 231, 238, 240, 243, 245, 246, 250, 252, 255

Offset: 1

Reinhard Zumkeller, Feb 25 2003

A080942(a(n))>2; complement of A080944;

A080942(a(n))-2 < A070824(a(n)).

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Cf. A080943, A080946, A007088, A080940, A080941.

a080945 n = a080945_list !! (n-1)
a080945_list = filter ((> 2) . a080942) [1..]
-- Reinhard Zumkeller, Mar 27 2014

cp's OEIS Frontend

A080943 Numbers having exactly two divisors that are also suffixes in binary representation.

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