A365780 - OEIS

A365780

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

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

(list; graph; refs; listen; history; text; internal format)

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

Table of n, a(n) for n=1..80.

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

Cf. A365768, A365769, A365781.

Sequence in context: A264090 A345283 A369750 * A297439 A168175 A164382

Adjacent sequences: A365777 A365778 A365779 * A365781 A365782 A365783

KEYWORD

nonn,easy,base,fini,full

AUTHOR

Eric Angelini, Sep 18 2023

EXTENSIONS

More terms from David A. Corneth, Sep 18 2023

STATUS

approved