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A365781 Lexicographically earliest permutation of the composite numbers such that a(n) - [the next digit] is a prime number. 2
4, 10, 8, 6, 12, 9, 20, 14, 15, 21, 22, 30, 16, 32, 18, 50, 33, 24, 51, 40, 34, 35, 42, 52, 54, 70, 36, 55, 25, 26, 38, 72, 56, 39, 27, 44, 74, 75, 28, 57, 45, 46, 58, 500, 90, 76, 91, 80, 77, 48, 78, 501, 200, 92, 93, 49, 60, 100, 300, 700, 94, 502, 301, 81, 82, 95, 62, 96, 702, 102, 104, 105, 84, 106, 98, 99, 201, 85, 63, 202, 302, 900 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
Is this sequence finite?
Yes, the sequence is finite. The last term is 900 as the previous prime before 900 is 887 and so the first digit of any next term is too small to reach 887. - David A. Corneth, Sep 18 2023
LINKS
EXAMPLE
a(1) = 4 and 4 - 1 = 3 (prime);
a(2) = 10 and 10 - 8 = 2 (prime);
a(3) = 8 and 8 - 6 = 2 (prime);
a(4) = 6 and 6 - 1 = 5 (prime);
a(5) = 12 and 12 - 9 = 3 (prime); etc.
PROG
(PARI) sequence() = {my(res = List([4]), n = 900, leftover = vector(n, i, 1), proceed = 1); leftover[1] = 0; leftover[4] = 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
Sequence in context: A298264 A014476 A080362 * A298400 A070295 A123483
KEYWORD
nonn,easy,base,fini,full
AUTHOR
Eric Angelini, Sep 18 2023
EXTENSIONS
More terms from David A. Corneth, Sep 18 2023
STATUS
approved

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Last modified May 17 19:53 EDT 2024. Contains 372607 sequences. (Running on oeis4.)