A359125
Largest prime factor of A359124(n).
Original entry on oeis.org
2, 13, 31, 19, 6173, 123457, 154321, 333667, 333667, 3388877, 4281283, 2630197, 26798700427, 8663199947, 2523244037, 12873492085621702963, 32929947197382727, 17539959825403, 71595329159622797, 325339942922532262019, 9999103057380477280607, 17465868005034957301, 1423364280511
Offset: 1
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FactorInteger[#][[-1,1]]&/@Table[FromDigits[Flatten[IntegerDigits/@Range[n]]]+1,{n,30}] (* Harvey P. Dale, Dec 20 2022 *)
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from sympy import factorint
def a(n): return max(factorint(int("".join(map(str, range(1, n+1)))) + 1))
print([a(n) for n in range(1, 24)]) # Michael S. Branicky, Dec 20 2022
A069048
Numbers k such that (i) k is a concatenation of consecutive natural numbers starting at 1 and (ii) k+1 is prime.
Original entry on oeis.org
1, 12, 123456, 123456789101112131415161718192021222324252627282930, 12345678910111213141516171819202122232425262728293031323334353637383940414243444546474849505152535455565758596061626364656667686970717273747576777879808182838485868788
Offset: 1
12 is a term since it is the concatenation of 1 and 2, and 12+1 = 13 is prime.
123456 is a concatenation, starting with 1, of consecutive natural numbers and 123456 + 1 = 123457 is prime.
k = 123456789101112131415161718192021222324252627282930 is a term since k+1 = 123456789101112131415161718192021222324252627282931 is prime.
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Select[Table[FromDigits[Flatten[IntegerDigits/@Range[n]]],{n,100}],PrimeQ[#+1]&] (* Harvey P. Dale, Dec 20 2022 *)
Showing 1-2 of 2 results.
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