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A344783
Numbers k such that 1 + Sum_{i=1..k} floor(k/i)*(2^i) is a prime number.
0
1, 3, 4, 7, 18, 25, 26, 30, 40, 50, 95, 150, 348, 694, 1052, 1222, 1808, 2567, 4917, 5399, 7438, 10720, 12152, 30412, 38313, 53620, 121419, 123523
OFFSET
1,2
COMMENTS
Equivalently, numbers k such that A168512(2^k) is a prime number.
The corresponding primes are 3, 19, 41, 283, 525529, 67117859, 134234921, 2147551801, ...
If k is a term of this sequence then 2^k * A168512(2^k) is a term of A168654 (see Ray Chandler's comment in A168654).
EXAMPLE
1 is a term since 1 + Sum_{i=1..1} floor(k/i)*(2^i) = 1 + 2 = 3 is a prime.
3 is a term since 1 + Sum_{i=1..3} floor(k/i)*(2^i) = 1 + 6 + 4 + 8 = 19 is a prime.
MATHEMATICA
Select[Range[100], PrimeQ[1 + Sum[Floor[#/i]*2^i, {i, 1, #}]] &]
CROSSREFS
Sequence in context: A361659 A331115 A327318 * A093611 A042375 A153067
KEYWORD
nonn,more
AUTHOR
Amiram Eldar, May 28 2021
EXTENSIONS
a(27)-a(28) from Michael S. Branicky, Sep 23 2024
STATUS
approved