OFFSET
0,2
LINKS
Reinhard Zumkeller (terms 0-300) & Antti Karttunen, Table of n, a(n) for n = 0..4095
FORMULA
a(0) = 1, a(2n) = nthcomposite(a(n)-1), a(2n+1) = nthprime(a(n)), where nthcomposite = A002808, nthprime = A000040. - Antti Karttunen, Apr 04 2015
PROG
(Haskell)
import Data.List (elemIndex); import Data.Maybe (fromJust)
a237739 = fromIntegral . (+ 1) . fromJust . (`elemIndex` a071574_list)
(PARI)
default(primelimit, (2^31)+(2^30));
A002808(n) = { my(k=-1); while( -n + n += -k + k=primepi(n), ); n }; \\ This function from M. F. Hasler
for(n=0, 4095, write("b237739.txt", n, " ", A237739(n)));
\\ Antti Karttunen, Apr 04 2015
(Scheme, with memoizing definec-macro)
(definec (A237739 n) (cond ((zero? n) 1) ((odd? n) (A000040 (A237739 (/ (- n 1) 2)))) (else (A002808 (+ -1 (A237739 (/ n 2)))))))
;; Antti Karttunen, Apr 04 2015
CROSSREFS
KEYWORD
nonn,look
AUTHOR
Reinhard Zumkeller, Apr 30 2014
EXTENSIONS
Name replaced by an explicit recurrence. - Antti Karttunen, Apr 04 2015
STATUS
approved