OFFSET
1,1
COMMENTS
Prime divisors are counted with multiplicity.
Similar to A155800, where k is restricted to primes.
Terms of the form 2^m-1 or 2^m+1 seem to occur frequently.
EXAMPLE
Adjacent to 2 are the numbers 1 and 3 which together have one prime divisor, hence a(1) = 2. Adjacent to 3 are 2 and 4; together they have three prime divisors, hence a(3) = 3. Adjacent to 4 are the primes 3 and 5, each having one prime divisor; hence a(2) = 4.
For k = 129, k-1 = 128 = 2*2*2*2*2*2*2 and k+1 = 130 = 2*5*13 together have ten prime divisors. For all numbers k < 129 the adjacent numbers k-1 and k+1 together have fewer or more than ten (for 127 there are eleven) prime divisors, hence a(10) = 129.
PROG
(PARI) {for(n=2, 150000000, s=bigomega(n-1)+bigomega(n+1); if(v[s]==0, v[s]=n)); v}
CROSSREFS
KEYWORD
nonn
AUTHOR
Klaus Brockhaus, Jan 28 2009, Jan 31 2009
EXTENSIONS
a(34)-a(37) from Donovan Johnson, Nov 02 2013
STATUS
approved