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A346651
a(n) is the number of divisors of A139245(n) ending with 2.
0
1, 2, 2, 2, 3, 2, 2, 3, 2, 2, 3, 3, 2, 4, 2, 2, 3, 2, 3, 4, 2, 2, 3, 2, 3, 5, 2, 3, 3, 2, 2, 4, 3, 2, 3, 4, 2, 4, 2, 3, 3, 2, 2, 5, 3, 2, 6, 2, 2, 4, 2, 3, 3, 3, 2, 4, 2, 4, 3, 3, 3, 5, 2, 2, 3, 2, 2, 7, 4, 2, 4, 2, 2, 4, 3, 3, 3, 2, 3, 6, 2, 3, 3, 4, 2, 4, 2, 2, 5, 2
OFFSET
1,2
COMMENTS
a(n) is odd if and only if A139245(n) either is the square of a number ending with 2 or has a unitary prime divisor ending with 7.
The term 1 appears only for n = 1 in corresponding to A139245(1) = 4.
EXAMPLE
a(14) = 4 since there are 4 divisors of A139245(14) = 264 ending with 2: 2, 12, 22 and 132.
MATHEMATICA
a[n_]:=Length[Drop[Select[Divisors[20n-16], (Last[IntegerDigits[#]]==2&)]]]; Array[a, 90]
PROG
(PARI) a(n) = sumdiv(20*n-16, d, (d%10) == 2); \\ Michel Marcus, Jul 26 2021
CROSSREFS
Cf. A000005, A017293 (numbers ending with 2), A017294 (squares of numbers ending with 2), A030432, A056169, A139245 (product of two numbers ending with 2), A346388, A346389.
Sequence in context: A103507 A219252 A290839 * A085694 A258570 A257572
KEYWORD
nonn,base
AUTHOR
Stefano Spezia, Jul 26 2021
STATUS
approved