A244748 Numbers k such that (product of digits of k)^2 + 1 is prime.

1, 2, 4, 6, 11, 12, 14, 16, 21, 22, 23, 25, 27, 28, 32, 38, 41, 44, 45, 46, 49, 52, 54, 58, 61, 64, 66, 69, 72, 78, 82, 83, 85, 87, 94, 96, 111, 112, 114, 116, 121, 122, 123, 125, 127, 128, 132, 138, 141, 144, 145, 146, 149, 152, 154, 158, 161, 164, 166, 169, 172, 178, 182, 183

Offset

1,2

Comments

A number k is a term of this sequence iff A007954(k)^2 is in A006093.

This sequence is infinite. With any number a(n), you can add infinitely many 1's to its decimal representation. E.g., 85 is in this sequence, so 185, 815, 851, 1185, 1815, 18115, etc. are terms as well.

Links

Jens Kruse Andersen, Table of n, a(n) for n = 1..10000

Example

(7*2)^2 + 1 = 197 is prime. Thus 72 is a term of this sequence.

Prog

(PARI) for(n=1, 10^3, d=digits(n); if(ispseudoprime(prod(i=1, #d, d[i])^2+1), print1(n, ", ")))

Crossrefs

Cf. A081988, A007954.

Sequence in context: A097954 A324333 A081988 * A245017 A300149 A171921

Adjacent sequences: A244745 A244746 A244747 * A244749 A244750 A244751

Keyword

nonn,base,easy

Author

Derek Orr, Jul 12 2014

Extensions

Corrected by Jens Kruse Andersen, Jul 13 2014

Status

approved