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 A308099 Numbers k with 2 or more chained distinct prime factors: the last digit of every prime factor is the same as the first digit of the next prime factor. Prime factors must be in ascending order. 3
 46, 58, 92, 93, 111, 116, 143, 184, 187, 209, 232, 265, 279, 295, 333, 368, 403, 422, 446, 454, 458, 464, 466, 478, 481, 482, 497, 502, 511, 514, 526, 538, 542, 553, 554, 562, 566, 586, 713, 736, 837, 844, 851, 892, 908, 916, 921, 928, 932, 933, 939, 951, 956, 964, 993, 999 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Robert Israel, Table of n, a(n) for n = 1..10000 EXAMPLE 144026 is such a number because its distinct prime factors in ascending order are 2, 23, 31, 101 and the last digit of each prime factor is the same as the first digit of the next one. MAPLE filter:= proc(n) local F, i;   F:= sort(convert(numtheory:-factorset(n), list));   nops(F) >= 2 and andmap(i -> F[i] mod 10 = floor(F[i+1]/10^ilog10(F[i+1])), [\$1..nops(F)-1]) end proc: select(filter, [\$1..1000]); # Robert Israel, Jun 21 2019 MATHEMATICA Select[Range@1000, PrimeNu@#>1&&And@@(Last@#[[1]]==First@#[[2]]&/@Partition[IntegerDigits@*First/@FactorInteger@#, 2, 1])&] PROG (PARI) isok(n) = {my(f=factor(n)[, 1]); if (#f <= 1, return(0)); my(vd=digits(f[1]), d=vd[#vd], vd2, d2); for (k=2, #f, vd2 = digits(f[k]); d2 = vd2[1]; if (d2 != d, return (0)); vd = vd2; d = vd[#vd]; ); return (1); } \\ Michel Marcus, May 18 2019 CROSSREFS Cf. A307858, A308252, A308101. Sequence in context: A330243 A326646 A332952 * A308252 A322161 A039424 Adjacent sequences:  A308096 A308097 A308098 * A308100 A308101 A308102 KEYWORD nonn,base AUTHOR Giorgos Kalogeropoulos, May 12 2019 STATUS approved

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Last modified November 28 01:24 EST 2021. Contains 349396 sequences. (Running on oeis4.)