A341887 a(n) = A341886(n)/2; numbers k such that A307437(k) is even.

256, 512, 1024, 2816, 4096, 5632, 8192, 11264, 27136, 28928, 48896, 54272, 61184, 65536, 75008, 82688, 84992, 90112, 94464, 97792, 105216, 122368, 124160, 128000, 138240, 139520, 150016, 158720, 166656, 167168, 167936, 168704, 176128, 183808, 185856, 195584

Offset

1,1

Comments

Indices of even terms in A307437; A341886 is the main entry.

Numbers k such that 2^k is a term: 8, 9, 10, 12, 13, 16, 18, 19, 20, 21, 22, 23, ... Are all sufficiently large powers of 2 terms? - Chai Wah Wu, Feb 24 2021

We don't know. From the comments in A341886, 2^k is a term if and only if t*2^(k+1)+1 is composite for t = 1, 2, 3. But we don't know if there are infinitely many Fermat primes. - Jianing Song, Feb 26 2021

All terms are divisible by 256. See my comment in A341886. - Jianing Song, Feb 27 2021

Links

Chai Wah Wu, Table of n, a(n) for n = 1..100

Example

psi(2048) = 512 is divisible by 2*256, and there is no odd m < 2048 such that 2*256 | psi(m), so 256 is a term.
psi(47104) = 5632 is divisible by 2*2816, and there is no m < 47104 such that 2*2816 | psi(m), so 2816 is a term.

Prog

(PARI) forstep(n=2, 10000, 2, if(A307437(n)%2==0, print1(n, ", "))) \\ see A307437 for its program

Crossrefs

Cf. A002322, A307437, A341886.

Sequence in context: A043336 A256822 A172422 * A031465 A045081 A294153

Adjacent sequences: A341884 A341885 A341886 * A341888 A341889 A341890

Keyword

nonn,hard

Author

Jianing Song, Feb 22 2021

Extensions

a(9)-a(20) from Michel Marcus, Feb 24 2021

a(21)-a(36) from Chai Wah Wu, Feb 24 2021

Status

approved