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A236675
If n is prime, then a(n) is the least composite number not occurring earlier, else a(n) is the least prime not occurring earlier.
3
2, 4, 6, 3, 8, 5, 9, 7, 11, 13, 10, 17, 12, 19, 23, 29, 14, 31, 15, 37, 41, 43, 16, 47, 53, 59, 61, 67, 18, 71, 20, 73, 79, 83, 89, 97, 21, 101, 103, 107, 22, 109, 24, 113, 127, 131, 25, 137, 139, 149, 151, 157, 26, 163, 167, 173, 179, 181, 27, 191, 28, 193
OFFSET
1,1
COMMENTS
If "composite" is replaced by "nonprime", one gets A026234, a permutation of the integers.
FORMULA
a(n) = A002808(A000720(n)) if n is prime, a(n) = A000040(n-A000720(n)) else.
PROG
(PARI) A236675=n->if(isprime(n), A002808(primepi(n)), prime(n-primepi(n)))
(PARI) c=p=1; vector(99, n, if(isprime(n), while(isprime(c++), ); c, p=nextprime(p+1)))
CROSSREFS
KEYWORD
nonn
AUTHOR
M. F. Hasler, Jan 29 2014
STATUS
approved