A073718 Powers of 2 with composite exponents.

16, 64, 256, 512, 1024, 4096, 16384, 32768, 65536, 262144, 1048576, 2097152, 4194304, 16777216, 33554432, 67108864, 134217728, 268435456, 1073741824, 4294967296, 8589934592, 17179869184, 34359738368, 68719476736

Offset: 1

Author

Labos Elemer, Aug 05 2002

Keywords

• easy
• nonn

Links

• Index to divisibility sequences

Crossrefs

Cf. A000079, A002808, A275306.

Programs

Mathematica

Table[2^FixedPoint[n+PrimePi[ # ]+1&, n], {n, 1, 30}]

PARI

for(n=4,100,if(!isprime(n),print1(2^n", "))) \\ Charles R Greathouse IV, Apr 09 2012

Formula

a(n) = 2^A002808(n) = A000079(A002808(n)).

Sum_{n>=1} 1/a(n) = A275306. - Amiram Eldar, Aug 11 2020