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 A350831 a(n) is the least positive integer not listed earlier such that its first digit together with a(n-1)'s last digit can form a prime; a(1) = 1. 1
 1, 3, 2, 9, 5, 31, 4, 7, 6, 11, 12, 32, 33, 8, 34, 13, 14, 15, 35, 36, 16, 17, 18, 37, 19, 21, 38, 39, 22, 91, 41, 42, 92, 93, 23, 24, 71, 43, 25, 94, 72, 95, 96, 73, 26, 74, 75, 97, 44, 76, 77, 45, 98, 99, 27, 46, 78, 301, 47, 48, 302, 303, 28, 304, 79, 29 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Conjectured to contain all positive integers not multiple of 10. LINKS Éric Angelini, Prime bayonets, personal web site "Cinquante signes" on blogspot.com, May 03 2022. PROG (PARI) u=[a=1]; vector(99, n, if(a>u[1]+1, u=setunion(u, [a]), u[1]=a; while(#u>1 && u[2]==u[1]+1+(u[1]%10==9), u=u[^1])); a%=10; my(k=u[1], d); n>1&& until(k++%10 && !setsearch(u, k) && (isprime(10*a+d=k\10^logint(k, 10)) || isprime(10*d+a)), ); a=k) CROSSREFS Cf. A350832 for a more complicated 2-digit variant. Sequence in context: A231442 A319107 A228323 * A140590 A329211 A164279 Adjacent sequences: A350828 A350829 A350830 * A350832 A350833 A350834 KEYWORD nonn,base AUTHOR M. F. Hasler and Eric Angelini, May 03 2022 STATUS approved

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Last modified March 29 18:37 EDT 2023. Contains 361599 sequences. (Running on oeis4.)