A356767 - OEIS

A356767

Tetraprimes (products of four distinct primes) whose reversals are different tetraprimes.

1518, 2046, 2226, 2262, 2418, 2478, 2618, 2622, 2814, 2838, 2886, 3135, 3927, 4170, 4182, 4386, 4389, 4746, 4785, 4935, 5313, 5394, 5406, 5478, 5565, 5655, 5838, 5874, 6018, 6045, 6222, 6402, 6438, 6474, 6486, 6690, 6699, 6834, 6846, 6882, 7293, 7458, 8106, 8142

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

COMMENTS

Palindromic tetraprimes are A046394.

The corresponding sequence for three distinct primes is A270175.

LINKS

Table of n, a(n) for n=1..44.

EXAMPLE

1518 = 2*3*11*23 is a tetraprime. Its reversal 8151 = 3*11*13*19 is another tetraprime. Thus, 1518 is in this sequence.

MATHEMATICA

Select[Range[10000], Transpose[ FactorInteger[FromDigits[Reverse[IntegerDigits[#]]]]][[2]] == {1, 1, 1, 1} && IntegerDigits[#] != Reverse[IntegerDigits[#]] && Transpose[FactorInteger[#]][[2]] == {1, 1, 1, 1} &]

PROG

(Python)

from sympy import factorint

def tetra(n): return list(factorint(n).values()) == [1, 1, 1, 1]

def ok(n):

if not tetra(n): return False

revn = int(str(n)[::-1])

return n != revn and tetra(revn)

print([k for k in range(9000) if ok(k)]) # Michael S. Branicky, Aug 27 2022

CROSSREFS

Cf. A046394, A270175.

Sequence in context: A257753 A236724 A206654 * A112641 A203386 A157375

Adjacent sequences: A356764 A356765 A356766 * A356768 A356769 A356770

KEYWORD

nonn,base

AUTHOR

Tanya Khovanova, Aug 26 2022

STATUS

approved