OFFSET
1,1
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..100
EXAMPLE
235=5*47 is semiprime and 532 is the 19th pentagonal number.
MATHEMATICA
Select[Range[60000], PrimeOmega[#]==2&&IntegerQ[(1+Sqrt[1+24* IntegerReverse[#]])/ 6]&] (* Harvey P. Dale, Apr 27 2022 *)
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Giovanni Resta, Jan 31 2006
STATUS
approved