

A251360


Numbers n such that n is the concatenation of prime factors of pi(n), in increasing order.


2




OFFSET

1,1


COMMENTS

Next term must be greater than 2*10^7.


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
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:
....p = q # Chai Wah Wu, Dec 10 2014, corrected Apr 04 2018


CROSSREFS



KEYWORD

nonn,base,more


AUTHOR



EXTENSIONS



STATUS

approved



