

A365780


Lexicographically earliest finite sequence of nonprime numbers such that a(n) + [the next digit] is a prime number.


2



1, 4, 9, 8, 30, 10, 12, 14, 32, 50, 33, 40, 15, 20, 34, 35, 6, 16, 18, 51, 21, 22, 70, 36, 52, 72, 74, 54, 55, 42, 56, 38, 39, 24, 57, 25, 44, 90, 75, 45, 26, 58, 91, 60, 76, 77, 27, 28, 92, 93, 46, 78, 100, 94, 95, 62, 96, 102, 104, 98, 99, 48, 500, 300, 700, 105, 49, 400, 106, 108, 110, 301, 63, 80, 302, 501, 81, 82, 111, 200
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OFFSET

1,2


COMMENTS

The sequence is finite. The last term is 200 as the next prime after 200 is 211 and so the first digit of any next term is too small to reach 211.  David A. Corneth, Sep 18 2023


LINKS



EXAMPLE

a(1) = 1 and 1 + 4 = 5 (prime);
a(2) = 4 and 4 + 9 = 13 (prime);
a(3) = 9 and 9 + 8 = 17 (prime);
a(4) = 8 and 8 + 3 = 11 (prime);
a(5) = 30 and 30 + 1 = 31 (prime); etc.


PROG

(PARI) sequence() = {my(res = List([1]), n = 700, leftover = vector(n, i, 1), proceed = 1); leftover[1] = 0; forprime(p = 2, n, leftover[p] = 0); while(proceed, for(i = 1, n, if(leftover[i] && isprime(res[#res] + digits(i)[1]), listput(res, i); leftover[i] = 0; next(2))); proceed = 0); res} \\ David A. Corneth, Sep 18 2023


CROSSREFS



KEYWORD

nonn,easy,base,fini,full


AUTHOR



EXTENSIONS



STATUS

approved



