OFFSET
0,1
COMMENTS
A098147 is difference between first odd semiprime > 10^n and 10^n. In this powers of 2 sequence, does 1 occur infinitely often? Does every odd number occur?
FORMULA
EXAMPLE
a(0) = 8 (the only even value here) because 2^0 + 8 = 9 = 3^2 is an odd semiprime.
a(1) = 7 because 2^1 + 7 = 9 = 3^2 is an odd semiprime.
a(2) = 5 because 2^2 + 5 = 9 = 3^2 is an odd semiprime.
a(3) = 1 because 2^3 + 1 = 9 = 3^2 is an odd semiprime.
a(4) = 5 because 2^4 + 5 = 21 = 3 * 7 is an odd semiprime.
a(5) = 1 because 2^5 + 1 = 33 = 3 * 11 is an odd semiprime.
a(6) = 1 because 2^6 + 1 = 65 = 5 * 13 is an odd semiprime.
a(10) = 3 because 2^10 + 3 = 1027 = 13 * 79 is an odd semiprime.
a(30) = 25 because 2^30 + 25 = 1073741849 = 29 * 37025581 is an odd semiprime.
MATHEMATICA
a[n_] := Block[{z}, If[n == 0, z = 3, z = 2^n + 1]; While[ PrimeOmega[z] != 2, z += 2]; z - 2^n]; a /@ Range[0, 64] (* Giovanni Resta, Jun 14 2016 *)
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Jonathan Vos Post, Feb 03 2006
EXTENSIONS
a(46) corrected by Giovanni Resta, Jun 14 2016
STATUS
approved