OFFSET
1,2
COMMENTS
Indices n such that A001358(n) and A091022(n) share at least one prime factor. - R. J. Mathar, Apr 26 2010
EXAMPLE
1 is a term because both semiprime(1)/2 = 4/2 = 2 and semiprime(semiprime(1))/2 = 10/2 = 5 are prime;
2 is a term because both semiprime(2)/3 = 6/3 = 2 and semiprime(semiprime(2))/3 = 15/3 = 5 are prime;
4 is a term because both semiprime(4)/2 = 10/2 = 5 and semiprime(semiprime(4))/2 = 26/2 = 13 are prime.
MAPLE
A091022 := proc(n) A001358(A001358(n)) ; end proc: seq(A091022(n), n=1..20) ; isA176654 := proc(n) pfsn := convert(numtheory[factorset]( A001358(n) ), list) ; pfsn1 := convert(numtheory[factorset]( A091022(n) ), list) ; op(1, pfsn) = op(1, pfsn1) or op(1, pfsn) = op(-1, pfsn1) or op(-1, pfsn) = op(1, pfsn1) or op(-1, pfsn) = op(-1, pfsn1) ; end proc: for n from 1 to 1600 do if isA176654(n) then printf("%d, ", n) ; end if; end do: # R. J. Mathar, Apr 26 2010
CROSSREFS
KEYWORD
nonn
AUTHOR
Juri-Stepan Gerasimov, Apr 22 2010
EXTENSIONS
Most values after a(6) replaced by R. J. Mathar, Apr 26 2010
STATUS
approved