A221860 Indices k such that prime(k) - k is a power of 2.

1, 2, 3, 15, 39, 2119, 4189897, 5812974437

Offset

1,2

Comments

The only primes in this sequence below primepi(10^8) are 2, 3 and 4189897.

prime(5812974437) - 5812974437 = 2^37. - Giovanni Resta, Apr 10 2013

a(9) > 1.4*10^16, if it exists. - Chai Wah Wu, Apr 24 2018

Links

Table of n, a(n) for n=1..8.

Re: 2^k - prime(p) or prime(p) - 2^k ?, SeqFan mailing list, Apr 10 2013

Formula

A000040(a(n))-a(n) = 2^floor(log[2](A000040(a(n)))) for all n>1.

Prog

(PARI) n=0; forprime(p=1, 10^8, n++; (t=p-n)==1<<valuation(t, 2)&print1(n", "))

Crossrefs

Cf. A014689.

Sequence in context: A143880 A037388 A298370 * A216339 A048076 A203432

Adjacent sequences: A221857 A221858 A221859 * A221861 A221862 A221863

Keyword

nonn,more

Author

M. F. Hasler, Apr 10 2013

Extensions

a(8) from Giovanni Resta, Apr 10 2013

Status

approved