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A251360 Numbers n such that n is the concatenation of prime factors of pi(n), in increasing order. 2
1117, 2163, 2537, 5137, 222926801 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
Next term must be greater than 2*10^7.
Numbers n such that n = A037276(A000720(n)).
a(6) > 4.5*10^9. - Chai Wah Wu, Dec 11 2014
Conjecture: a(n) are numbers n such that n = A084317(A000720(n)). - Chai Wah Wu, Apr 04 2018
LINKS
Chris Caldwell, G. L. Honaker and Lewis, 1117
EXAMPLE
1117 is in the sequence since pi(1117) = 11*17,
2163 is in the sequence since pi(2163) = 2*163,
2537 is in the sequence since pi(2537) = 2*5*37,
and 5137 is in the sequence since pi(5137) = 5*137.
MATHEMATICA
a251360[n_Integer] := Select[Range[n], # ==
FromDigits[Flatten@IntegerDigits[First@ Transpose@ FactorInteger[PrimePi[#]]]] &]; a251360[10^5] (* Michael De Vlieger, Dec 03 2014 *)
PROG
(Python)
from sympy import prime, factorint
A251360_list, p = [], 3
for n in range(2, 10**6):
....q, fn = prime(n+1), factorint(n)
....m = int(''.join(str(d)*fn[d] for d in sorted(fn)))
....if p <= m < q:
........A251360_list.append(m)
....p = q # Chai Wah Wu, Dec 10 2014, corrected Apr 04 2018
CROSSREFS
Sequence in context: A161848 A020380 A243527 * A201034 A264312 A145334
KEYWORD
nonn,base,more
AUTHOR
Jahangeer Kholdi, Dec 01 2014
EXTENSIONS
a(5) from Chai Wah Wu, Dec 10 2014
STATUS
approved

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Last modified May 26 21:09 EDT 2024. Contains 372844 sequences. (Running on oeis4.)