A379938 Numbers k such that the k-th prime is a power of two reversed.

1, 9, 18, 142, 575, 23652, 3633466, 10846595429, 802467018101, 2289255503212477

Offset: 1

Author

Kalle Siukola, Jan 06 2025

Keywords

• base
• nonn
• more

Examples

			The 9th prime is 23, 23 reversed is 32, and 32 = 2^5, so 9 is a term.
		

Crossrefs

Cf. A000040, A000079, A004087, A004094, A057708, A102385.

Programs

Python

import sympy
for (k, p) in enumerate(sympy.primerange(10**8)):
    rev = int(str(p)[::-1])
    # is rev a power of two (or zero)?
    if rev & (rev - 1) == 0:
        print(k + 1, end=",")
print()

Formula

A000040(a(n)) = A102385(n).

a(n) = A000720(A102385(n)). - Michel Marcus, Jan 07 2025

Extensions

a(8)-a(10) from Amiram Eldar, Jan 07 2025