A251360 Numbers n such that n is the concatenation of prime factors of pi(n), in increasing order.

1117, 2163, 2537, 5137, 222926801

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

Table of n, a(n) for n=1..5.

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

Cf. A000040, A000720, A251361, A251362.

Sequence in context: A161848 A020380 A243527 * A201034 A264312 A145334

Adjacent sequences: A251357 A251358 A251359 * A251361 A251362 A251363

Keyword

nonn,base,more

Author

Jahangeer Kholdi, Dec 01 2014

Extensions

a(5) from Chai Wah Wu, Dec 10 2014

Status

approved