A120805
Primes with consecutive digits.
Original entry on oeis.org
2, 3, 5, 7, 23, 43, 67, 89, 109, 4567, 10987, 76543, 78901, 678901, 23456789, 45678901, 9012345678901, 789012345678901, 56789012345678901234567890123, 90123456789012345678901234567, 10987654321098765432109876543210987
Offset: 1
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f[n_] := Block[{u = Range@n, d = Reverse@ Range@n, t = Table[1, {n}]}, Select[ Drop[ Union@ Flatten@ Table[ FromDigits /@ Mod[{u, d} + {i*t, i*t}, 10], {i, 10}], 2], PrimeQ@# &]]; Array[f, 35] // Flatten
A215477
Semiprimes with consecutive (ascending) digits.
Original entry on oeis.org
4, 6, 9, 34, 123, 789, 901, 1234, 34567, 56789, 901234, 1234567, 7890123, 567890123, 12345678901, 345678901234567, 4567890123456789, 12345678901234567, 890123456789012345, 3456789012345678901, 456789012345678901234, 123456789012345678901234567, 1234567890123456789012345678901, 23456789012345678901234567890123
Offset: 1
a(9) = 34567 because it is semiprime 13 * 2659, and (3,4,5,6,7) are consecutive ascending digits.
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R:= 4, 6, 9: V:= [$1..9]:
for d from 2 to 50 do
V:= map(n -> 10*n + ((n+1) mod 10), V);
W:= select(t -> numtheory:-bigomega(t)=2, V);
R:= R, op(W);
od:
R; # Robert Israel, Nov 15 2023
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