login
A102181
Iccanobirt semiprime indices (11 of 15): Indices of semiprime numbers in A102121.
1
5, 11, 12, 17, 18, 37, 38, 43, 44, 45, 55, 61, 70, 93, 103, 110, 120, 129, 174, 198, 241, 245, 277, 303, 342, 381, 393, 552, 590, 657, 708
OFFSET
1,1
FORMULA
A102121(a(n)) = A102201(n).
MATHEMATICA
nxt[{a_, b_, c_}]:={b, c, IntegerReverse[c+IntegerReverse[b]+IntegerReverse[a]]}; Flatten[ Position[NestList[nxt, {0, 0, 1}, 800][[;; , 1]], _?(PrimeOmega[#]==2&)]-1] (* Harvey P. Dale, Mar 23 2023 *)
CROSSREFS
KEYWORD
nonn,more,less,base
AUTHOR
EXTENSIONS
Offset changed to 1 and a(21)-a(31) from Jinyuan Wang, Aug 14 2021
STATUS
approved